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Red corpuscles (blood cells) of the frog. The red blood cells of birds, reptiles, amphibians and fishes are oval and contain a nucleus in the center that is not found in human red corpuscles.

Blood Cells

Red corpuscles (blood cells) of the frog. The red blood cells of birds, reptiles, amphibians and fishes…

White blood corpuscle (cell), sketched at successive intervals of a few seconds to illustrate the changes of form due to its amoeboid movements.

Blood Cells

White blood corpuscle (cell), sketched at successive intervals of a few seconds to illustrate the changes…

Origin of lymphatics. Labels: S, lymph spaces communicating with lympathic vessel; A, origin of lymphatic by union of lymp spaces; E, E, endothelial cells forming wall of lymph vessel.

Lymphatics

Origin of lymphatics. Labels: S, lymph spaces communicating with lympathic vessel; A, origin of lymphatic…

Circulation in frog's foot under a microscope. Labels: A, walls of capillaries; B, tissue of web lying between the capillaries; C, cells of epidermis covering web (these are only shown in the right-hand and lower part of the field; in the other parts of the field the focus of the microscope lies below the epidermis); D, nuclei of these epidermic cells; E, pigment cells contracted, not partially expanded; F, red blood corpuscle (oval in the frog) passing along capillary -- nucleus not visible; G, another corpuscle squeezing its way through a capillary, the canal of which is smaller than its own transverse diameter; H, another bending as it slides round a corner; K, corpuscle in capillary seen through the epidermis; I, white blood corpuscle.

Circulation in a Frog's Foot

Circulation in frog's foot under a microscope. Labels: A, walls of capillaries; B, tissue of web lying…

A section through the epidermis, somewhat diagrammatic, highly magnified. Below is seen a papilla of the dermis, with its artery, f, and veins, gg; a, the horny layer of the epidermis; b, the rete muscosum or Malpighian layer; d, the layer of columnar epidermic cells in immediate contact with the dermis; h, the duct of a sweat gland.

Epidermal Section

A section through the epidermis, somewhat diagrammatic, highly magnified. Below is seen a papilla of…

Magnified view of the epidermis, showing mouths of the sweat glands.

Epidermis

Magnified view of the epidermis, showing mouths of the sweat glands.

A thin transverse section of half the spinal cord magnified about 10 diameters. Labels: 1, anterior fissure; 2, posterior fissure; 3, central canal ;8, pia mater enveloping the cord; 6,7, bands of pia mater penetrating the cord and supporting its nerve elements; 9, a posterior root; 10, bundles of an anterior root; a,b,c,d,e, groups of nerve cells in the gray matter.

Spinal Cord Section

A thin transverse section of half the spinal cord magnified about 10 diameters. Labels: 1, anterior…

Section of skin showing two papillae of the dermis and some of the deeper cells of the epidermis, involved in sensation of the skin. Labels: a, papilla containing blood vessels; b, papilla containing a tactile corpuscle, t; d, medullated nerve fibers going to the corpuscle; at f, optical cross-sections of the fibers are seen as they wind round the outside of the corpuscle; the general transverse direction of the connective tissue bundles of the capsule of the corpuscle is shown.

Sensation of the Skin

Section of skin showing two papillae of the dermis and some of the deeper cells of the epidermis, involved…

Cells from the olfactory epithelium. Labels: 1, from the frog. 2, from the man; a, columnar cell, with its branched deep process; b, so-called olfactory cell; c, its narrow outer process; d, its slender central process. 3, gray nerve fibers of the olfactory nerve, seen dividing into fine peripheral branches at a.

Olfactory Epithelium

Cells from the olfactory epithelium. Labels: 1, from the frog. 2, from the man; a, columnar cell, with…

Forms of nerve cells. Labels: A, from spinal ganglion; B, from ventral horn of spinal cord; C, pyramidal cell from cerebral cortex; D, Purkinje cell from cerebellar cortex; E, Golgi cell of type II from spinal cord; F, fusiform cell from cerebral cortex; G, sympathetic; a, axon; d, dendrites; c, collateral branches; ad, apical dendrites; bd, basal dendrites; c, central process; p, peripheral process.

Nerve Cells

Forms of nerve cells. Labels: A, from spinal ganglion; B, from ventral horn of spinal cord; C, pyramidal…

Structure of the human retina, showing the various layers.

Structure of the Retina

Structure of the human retina, showing the various layers.

The lamina reticularis, which is a delicate perforated membrane which extends from the articulations of the rods outward to the external row of the outer hair cells. It is part of the Organ of Corti (organon spirale), also known as the Papilla Spiralis.

The Lamina Reticularsis

The lamina reticularis, which is a delicate perforated membrane which extends from the articulations…

Structure of the teeth. A tooth consists of 3 structures, the dentine (2), or ivory, the proper dental substance, forming the larger portion; the enamel or adamant (3), a layer covering the crown; and the cement (1), a thin layer on the surface of the fang. A central chamber, the pulp-cavity, occupies the interior, and contains the pulp, a soft, vascular, and sensitive organ, surrounded by a layer of cells, the odonto-blasts, or dentine-forming cells.

Structure of the Teeth

Structure of the teeth. A tooth consists of 3 structures, the dentine (2), or ivory, the proper dental…

Lobules of the liver (1), which are small, granular-looking bodies, of polygonal shape, and about 1/20 inch in diameter, clustered around the sublobular branches of the hepatic veins, and connected together by connective tissue (3), blood-vessels, ducts (2), and lymphatics. Each lobule consists of a mass of hepatic cells, surrounded by a dense capillary plexus, and contains the minute beginnings of a bile-duct, the so-called biliary capillaries; possessing therefore all the essential constituents of a secreting gland. A lobule contains hepatic cells, lobular veins (3), intralobular veins (4), and plexuses of lymphatics, nerves, and bile-ducts.

Lobules of the Liver

Lobules of the liver (1), which are small, granular-looking bodies, of polygonal shape, and about 1/20…

Structure of the lung. The lung has a serous coat; a sub-serous, elastic areolar tissue, investing the entire organ, and extending inward between the lobules; and the parenchyma, or true lung-tissue, composed of lobules and alveoli (or air-cells).

Structure of the Lungs

Structure of the lung. The lung has a serous coat; a sub-serous, elastic areolar tissue, investing the…

Fat vesicles in adipose (fatty) tissue. Adipose tissue is a subtype of connective tissue consisting of a growth of small sacs containing fat bound together by connective tissue and small blood vessels.

Adipose Tissue

Fat vesicles in adipose (fatty) tissue. Adipose tissue is a subtype of connective tissue consisting…

Fibrous cartilage connective tissue from the symphysis pubis, magnified. Cartilage is a structure without blood vessels and nerves, containing cells lying in a dense substance, which on boiling becomes jelly-like, resembling glue. It is mainly found in the joints, but also in the ear, nose, and air passages of the chest.

Cartilage Tissue

Fibrous cartilage connective tissue from the symphysis pubis, magnified. Cartilage is a structure without…

Columnar epithelium lining a gland. It consists of conical cells laid side by side, their ends forming the surface of the membrane and is found in the stomach, intestines, and elsewhere.

Columnar Epithelial Tissue

Columnar epithelium lining a gland. It consists of conical cells laid side by side, their ends forming…

Forms of nerve cells. They each have a nucleus and nucleolus and are connected to each other by means of numerous branches and are found in the brain, spinal cords, and other nerves.

Nerve Cells

Forms of nerve cells. They each have a nucleus and nucleolus and are connected to each other by means…

A diagram of nerve tubules A nerve tube consists of a white portion which is fatty, and which protects the central portion, or axis cylinder. Surrounding these is a tubular membrane composed of epithelial cells. The nerve of the body are made up of bundles of these tubes, bound together by connective tissue and enclosed in a sheath of the same. Labels: a, axis cylinder; b, inner border of white substance; c, c, outer border of same; d, ,d, tubular membrane; B, tubular fibers; e, in natural state; f, under pressure; g, g', varicose fibers.

Nerve Tubules

A diagram of nerve tubules A nerve tube consists of a white portion which is fatty, and which protects…

Diagram showing the structure of the lungs. At <em>d</em> is the left lung, and at <em>c</em> are represented the main branch of the windpipe that go to the right lung, separated by the lung itself. At the lower part, at <em>e</em>, are represented the very minute branches as they go to the air-cells (alveoli). At <em>b</em> is the windpipe (trachea), and at <em>a</em> is the larynx (or Adam's apple). It is through a chink in this that air passes in and out as we breathe.

Structure of the Lungs

Diagram showing the structure of the lungs. At d is the left lung, and at c are represented…

Flat epithelium cells from the surface of the peritoneum. Labels: a, cell body; c, nucleus.

Flat Epithelium Cells

Flat epithelium cells from the surface of the peritoneum. Labels: a, cell body; c, nucleus.

Connective tissue cells: a, from areolar tissue; b, from tendon.

Connective Tissue Cells

Connective tissue cells: a, from areolar tissue; b, from tendon.

A thin slice of cartilage, magnified, to how the cells embedded in the homogenous matrix. Labels: a, cell in which the nucleus has divided; b, a cell in which division is just complete; c, e, a group of four cells resulting from further division of a pair like b; the new cells have formed some matrix between them, separating them from another; d, d, cavities in the matrix from which cells have dropped out during the preparation of the specimen.

Cartilage Tissue Cells

A thin slice of cartilage, magnified, to how the cells embedded in the homogenous matrix. Labels: a,…

Isolated smooth muscle cells of the small intestine.

Smooth Muscle Cells

Isolated smooth muscle cells of the small intestine.

Ciliated cells, such as those lining the windpipe.

Ciliated Cells

Ciliated cells, such as those lining the windpipe.

Blood corpuscles (cells). Labels: A, magnified about 400 diameters. The red corpuscles have arranged themselves in rouleaux; a, a, colorless corpuscle; B, red corpuscles more magnified and seen in focus; E, a red corpuscle slightly out of focus. Near the right -hand top corner is a red corpuscle seen in three-quarter face, and at C one is seen edgewise. F, G, H, I, white corpuscles highly magnified.

Blood Corpuscles

Blood corpuscles (cells). Labels: A, magnified about 400 diameters. The red corpuscles have arranged…

A white blood corpuscle sketched at successive intervals of a few seconds to illustrate the change of form due to tis amoeboid movements.

White Blood Corpuscle

A white blood corpuscle sketched at successive intervals of a few seconds to illustrate the change of…

A lobule of a pig liver, magnified, showing the hepatic cells radially arranged around the central intralobular vein, and the connective tissue surrounding the lobule.

Liver Lobule of a Pig

A lobule of a pig liver, magnified, showing the hepatic cells radially arranged around the central intralobular…

Diagram to illustrate the relationship of blood capillaries, bile capillaries, and liver cells. Labels: L, intralobular vein at center of lobule; P, vessel of interlobular plexus from which a blood capillary extends to L; D, a minute bile duct with which a bile capillary communicates.

Liver Structure

Diagram to illustrate the relationship of blood capillaries, bile capillaries, and liver cells. Labels:…

Diagram showing a kidney glomerulus and the commencement of an uriniferous tubule. Labels: a, afferent blood vessel pushing in the wall, w, of a Malpighian capsule and ending in the capillary tuft from which the vein e issues; c, involuted epithelium the vascular tuft, but in nature it forms a close investment around each vessel of the glomerulus; A, space in capsule into which liquid transuded from the vessel of the glomerulus passes; d, neck of capsule passing into commencement of first convoluted portion, f f, of an uriniferous tubule; o, granular epithelial cells; b, basement membrane.

Kidney Glomerulus and Uriniferous Tubule

Diagram showing a kidney glomerulus and the commencement of an uriniferous tubule. Labels: a, afferent…

A section through the epidermis, highly magnified. Labels: Below is seen a papilla of the dermis, with its artery, f, and veins, g g; a, the horny layer of the epidermis; b, the rete mucosum or Malpighian layer; d, the layer of columnar epidermic cells in immediate contact with the dermis; h, the duct of a sweat gland.

Epidermis and Sweat Gland

A section through the epidermis, highly magnified. Labels: Below is seen a papilla of the dermis, with…

Red and white blood corpuscles (cells).

Red and White Blood Cells

Red and white blood corpuscles (cells).

Human liver cells.

Liver Cells

Human liver cells.

The above cut represents a section of the thigh bone. The extremities (a, w) having a shell or thin plate of compact texture, crowded with small cells, diminishing in size, but increasing in number as they approach the articulation (c), the cavity for containing the marrow; the walls of the shaft are very firm and solid (b, b). The compact part is thickest near the middle of the bone where the greatest strength is required.

Thigh Bone Section

The above cut represents a section of the thigh bone. The extremities (a, w) having a shell or thin…

In Roman mythology, Pluto was the god of the dead. Cerberus was his dog who guard the underworld.

Pluto and Cerberus

In Roman mythology, Pluto was the god of the dead. Cerberus was his dog who guard the underworld.

"A, embryonic cells from onion root tip; d, plasmatic membrane; c, cytoplasm; a, nuclear membrane enclosing the thread-like nuclear reticulum; b, nucleolus; e, plastids (black dots scattered about)." -Stevens, 1916

Onion Cells

"A, embryonic cells from onion root tip; d, plasmatic membrane; c, cytoplasm; a, nuclear membrane enclosing…

"B, older (onion) cells farther back from the root tip. The cytoplasm is becoming vacuolate; f, vacuole." -Stevens, 1916

Onion Cells

"B, older (onion) cells farther back from the root tip. The cytoplasm is becoming vacuolate; f, vacuole."…

In onion cells: "C, a cell from the epidermis of the mid-rib of Tradescantia zebrina, in its natural condition on the right, and plasmolyzed by salt solution on the left; g, space left by the recedence of the cytoplasm from the wall; the plasma membrane can now be seen as a delicate membrane bounding the shrunken protoplast." -Stevens, 1916

T. Zebrina Cell

In onion cells: "C, a cell from the epidermis of the mid-rib of Tradescantia zebrina, in its natural…

"B, cells from the petal of Lupinus luteus with yellow chromoplasts." -Stevens, 1916

L. Luteus Cell

"B, cells from the petal of Lupinus luteus with yellow chromoplasts." -Stevens, 1916

"Group of cells from petal of Viola tricolor." -Stevens, 1916

Plant Epidermis

"Group of cells from petal of Viola tricolor." -Stevens, 1916

"Two epidermal cells in cross section showing thickened outer wall differentiated into three layers, namely, an outer cuticle, cutinized layer (shaded), and an inner cellulose layer." -Stevens, 1916

Plant Epidermis

"Two epidermal cells in cross section showing thickened outer wall differentiated into three layers,…

"Epidermal outgrowths in the form of scales and hairs." -Stevens, 1916

Plant Epidermis

"Epidermal outgrowths in the form of scales and hairs." -Stevens, 1916

"Epidermal outgrowths in the form of scales and hairs." -Stevens, 1916

Plant Epidermis

"Epidermal outgrowths in the form of scales and hairs." -Stevens, 1916

"Cross section of a portion of leaf of Ficus elastica showing the multiple epidermis from e to a inclusive; c, cystolith; b, palisade parenchyma; d, spongy parenchyma." -Stevens, 1916

F. Elastica Epidermis

"Cross section of a portion of leaf of Ficus elastica showing the multiple epidermis from e to a inclusive;…

First developmental stage of stone cells: "1, in the primary meristem condition." -Stevens, 1916

Stone Cells 1

First developmental stage of stone cells: "1, in the primary meristem condition." -Stevens, 1916

Second developmental stage of stone cells: "2, the cells have enlarged and the walls have begun to thicken and become pitted." -Stevens, 1916

Stone Cells 2

Second developmental stage of stone cells: "2, the cells have enlarged and the walls have begun to thicken…

Third and final developmental stage of stone cells: "3, The walls are completed. The primary wall is black, cellulose additions white, and the lignified walls in 3 are stippled. Notice that the protoplasts have disappeared in 3, and the pits in some instances are branched." -Stevens, 1916

Stone Cells 3

Third and final developmental stage of stone cells: "3, The walls are completed. The primary wall is…

Developmental stages of bast fibers: "1 and 2, cross and longitudinal sections of primary meristem cells that are to become bast fibers." -Stevens, 1916

Bast Fibers 1 and 2

Developmental stages of bast fibers: "1 and 2, cross and longitudinal sections of primary meristem cells…

Developmental stages of bast fibers: 3 and 4, cross and longitudinal sections of meristem cells becoming bast fibers.

Bast Fibers 3 and 4

Developmental stages of bast fibers: 3 and 4, cross and longitudinal sections of meristem cells becoming…

Developmental stages of bast fibers: "5, longitudinal section of completed bast fibers. In 5 the stippling of the wall indicates lignification. Note that the walls have become pitted and the protoplasts have disappeared from the fibers." -Stevens, 1916

Bast Fibers 5

Developmental stages of bast fibers: "5, longitudinal section of completed bast fibers. In 5 the stippling…

"Portion of a cross section of a root of Allium ascalonicum. h, large central, tracheal tube; i, xylem, and l, phloem portion of the vascular bundle; n, cortex cells; 1, endodermis with thin-walled cell at k to admit passage of materials; m, pericycle or pericambium." -Stevens, 1916

A. Ascalonicum Root

"Portion of a cross section of a root of Allium ascalonicum. h, large central, tracheal tube; i, xylem,…

"Diagram to show different plans in the distribution of bast fibers. A, bast a continuous cylinder in the pericycle; B, isolated strands of bast in the cortex and in the pericycle in front of each vascular bundle; C, a combination of A and B." -Stevens, 1916

Bast Fibers

"Diagram to show different plans in the distribution of bast fibers. A, bast a continuous cylinder in…

First developmental stage of sieve tubes, companion cells, and phloem parenchyma. "A, a and b, two rows of procambial cells; in c and d, a has divided longitudinal and c is to become companion cells; d, a sieve tube, and b, phloem parenchyma." -Stevens, 1916

Plant Cell Development 1

First developmental stage of sieve tubes, companion cells, and phloem parenchyma. "A, a and b, two rows…

Second developmental stage of sieve tubes, companion cells, and phloem parenchyma. "B, c, companion cells, and d, a beginning sieve tube from c and d, respectively in A. The cross-walls in d are pitted; b, phloem parenchyma grown larger." -Stevens, 1916

Plant Cell Development 2

Second developmental stage of sieve tubes, companion cells, and phloem parenchyma. "B, c, companion…

Third developmental stage of sieve tubes, companion cells, and phloem parenchyma. "The pits in the cross-walls of the sieve tubes become perforations, and the nuclei gone from the cells composing the tube." -Stevens, 1916

Plant Cell Development 3

Third developmental stage of sieve tubes, companion cells, and phloem parenchyma. "The pits in the cross-walls…

"Stages in the development of the elements of the xylem. A, progressive steps in the development of a tracheal tube. 1, row of procambial or cambial cells that are to take part in the formation of a tube; 2, the same at a later stage enlarged in all dimensions; 3, the cells in 2 have grown larger, their cross-walls have been dissolved out, and the wall has become thickened and pitted; 4, the walls in 3 have become more thickened, the pits have an overhanging border, the walls have become lignified as indicated by the stippling, and finally the protoplasts have disappeared, and the tube is mature and dead." -Stevens, 1916

Xylem Development 1

"Stages in the development of the elements of the xylem. A, progressive steps in the development of…

Stages in the development of the elements of the xylem. "B, stages in the formation of tracheids from procambial or cambial cells. The steps are the same as in A, excepting that the cross-walls remain and become pitted." -Stevens, 1916

Xylem Development 2

Stages in the development of the elements of the xylem. "B, stages in the formation of tracheids from…

Stages in the development of the elements of the xylem. "C, steps in the development of wood fibers from cambial cells; 1, cambial cells; 2, the same grown larger in all dimensions with cells shoving past each other as they elongate; 3, a later stage with cells longer and more pointed and walls becoming thickened and pitted; 4, complete wood fibers with walls more thickened than in the previous stage and lignified, as shown by the stippling. The protoplasts in this last stage have disappeared and the fibers are dead." -Stevens, 1916

Xylem Development 3

Stages in the development of the elements of the xylem. "C, steps in the development of wood fibers…

Stages in the development of the elements of the xylem. "D, steps in the formation of wood parenchyma from cambial or procambial cells. 1, group of cambial or procambial cells; 2, the same enlarged in all dimensions; 3, the same with walls thickened and pitted; 4 and 5 show the same stages as 2 and 3, but here the cells have enlarged radially or tangentially more than they have vertically. The walls of these cells are apt to become lignified, but the cells are longer lived than the wood fibers." -Stevens, 1916

Xylem Development 4

Stages in the development of the elements of the xylem. "D, steps in the formation of wood parenchyma…