This diagram shows some stages in the life history of the tapeworm. A, Cysticercus or Bladderworm stage, before the "head" protrudes from the bladder; B, same, later stage; C, Strobila, or chain of proglottides, many being omitted; D, embryo such as fill the uterus of the mature proglottides. It is protected by a shell. b, bladder; ex., excretory canals; g, genital pore; h, head or scolex provided with hooks and suckers (s); u, uterus in a mature posterior proglottis; z, one of budding or segment formation. The numerals show the approximate number of segments, reckoning from the front.