598 



CESTOIDEA 



the last proglottis, where they open to the exterior. In the originally pos- 

 terior proglottis there is a pear-shaped excretory vesicle in the middle of the 

 posterior edge, but this arrangement is lost when this proglottis drops off, and 

 then the tubes open as a rule separately on the last proglottis. The nervous 

 system consists of one ganglion in the scolex and two nerve cords. The 

 generative organs gradually develop in the proglottides as they grow older, 

 the youngest having no trace of them. With the exception of the end por- 

 tions, these organs lie in the medullary layer of the body. 



The male organs, which are the first to reach maturity, usually consist of 

 numerous follicular testes scattered over the dorsal portion of the medullary 

 layer, but may be consolidated into one to three glands. The efferent ducts 

 from these unite about the middle of the proglottis into a vas deferens, which, 

 after a wavy convoluted course, enters a cirrus pouch and terminates in the 

 genital atrium near the vaginal orifice. 



The female reproductive organs consist usually of two ovaries, which lie 

 near the ventral surface of the medullary layer, from which a common oviduct 

 runs to join with the spermatic duct, which, after travelling a certain distance, 

 is dilated to form a eceptaculum seminis, and continued as the vagina to the 

 female opening in the genital atrium. After the junction with the spermatic 

 duct, the oviduct is joined by the common duct of the yolk or vitellogene 

 gland or glands, and then, forming the ootype, receives the ducts of the shell 

 gland, and passes on to enter the uterus. This is usually a blind tube, but 

 may open by a special aperture on the same or the opposite surface to that on 

 which the genital atrium is found. 



When the uterus becomes laden with eggs, it is apt to alter its appearance 

 and become branched, and grows, filling up the proglottis, while the male 

 generative organs atrophy and disappear {vide Fig. 253, p. 614). 



Life-History.— The proglottis can fertilize itself with or without 

 the use of the cirrus, or different proglottides may fertilize one 

 another. In any case, the receptaculum seminis receives the sper- 

 matozoa, which travel down the spermatic duct, and, meeting the 



" F^CAL Egg of 



Fig. -240. — Uterine Egg of TcBnia Fig. 241. — Ovum Tania solium. 



ovum, fertilize it. The fertilized ovum now obtains its yolk 

 (vitellus) and its shell, and then passes into the uterus, from which 

 it may escape by the uterine orifice when there is one, or not until 

 the proglottis is destroyed . 



Development usually begins in the uterus. An egg is as a rule 

 oval in form, enclosed in a brown or yellow shell with or without 

 an operculum. This shell contains food yolk and the developing 

 embryo, whose cells form two membranes — an outer in contact with 

 the shell, and an inner in contact with the embryo. 



saginata. (X 375-) 

 (After Leuckart.) 



OF Dibothrio- 

 cephalus latus. 



(After Leuckart.) 



(X300)- 

 (After Leuc- 

 kart.) 



