"Daphnia. E., Eye; A.2, second antenna; A.1, first antenna; dg., digestive caeca; s.g., shell gland; go., gonad; h., heart in pericardium; o., ovum; B.p., brood-pouch; sp., spine; f., furca; s., setae; Ab., rudimentary abdomen; t., caudal fork; g., gut; 1-5, thoracic limbs." -Thomson, 1916

Daphnia

"Daphnia. E., Eye; A.2, second antenna; A.1, first antenna; dg., digestive caeca; s.g., shell gland;…

Diagram of a longitudinal section of an embryo, showing the different areas of the blastodermic vesicle. Labels: a, pericardium; b, bucco-pharyngeal; c, ectoderm; d, entoderm; e,placental area.

Longitudinal Section of an Embryo

Diagram of a longitudinal section of an embryo, showing the different areas of the blastodermic vesicle.…

View of the heart enclosed in its bag, or pericardium, which is a serious membrane. It is here laid open and turned back.

Heart in the Pericardium

View of the heart enclosed in its bag, or pericardium, which is a serious membrane. It is here laid…

Diagram of a developing ovum, seen in longitudinal section. Labels: a, pericardium; b, bucco-pharyngeal; c, ectoderm; d, entoderm; e,placental area. f, spinal cord; i, brain; g, notochord; k, extra embryonic coelom; h, dorsal wall of alimentary canal.

Developing Ovum

Diagram of a developing ovum, seen in longitudinal section. Labels: a, pericardium; b, bucco-pharyngeal;…

"View from below of a scorpion (Buthus occitanus) opened and dissected so as to show the pericardium with its muscles, the lateral arteries, and the tergo-sternal muscles. PRO, Prosoma. dpm, Dorso-plastral muscle. art, Lateral artery. tsm1, Tergo-sternal muscle of the second (pectiniferous) mesosomatic somite; this is the most anterior pair of the series of six, none are present in the genital somite. tsm4, Tergo-sternal muscle of the fifth mesosomatic somite. tsm6, Tergo-sternal muscle of the enlarged first metasomatic somite. Per, Pericardium. VPM1 to VPM7, The series of seven pairs of veno-pericardiac muscles. There is some reason to admit the existence of another more anterior pair of these muscles in Scorpio; this would make the number exactly correspond with the number in Limulus." — The Encyclopedia Britannica, 1910

Scorpion

"View from below of a scorpion (Buthus occitanus) opened and dissected so as to show the pericardium…

The thymus gland in a full term fetus.

Thymus Gland

The thymus gland in a full term fetus.