.324 DESCRIPTION OF THE PLATES. 



FIG. 2. Posterior half of an unripe segment of Taenia coenurus, to show the generative 

 organs, male and female; after Leuckart, Die Menschlichen Parasiten, ed. 2, p. 399, Fig. 165. 



a. Water-vascular or excretory canal. Two vessels, a dorsal and ventral, 



one of which is much larger than the other, and is not shown 

 here, run along either side of each segment, parallel with and 

 close to each other, and are connected with their fellows on the 

 opposite side of each segment by a transverse anastomosis. This 

 transverse connecting vessel takes in the last segment the shape 

 of a median vesicle into which the lateral vessels converge, and 

 through which they open to the exterior. In the larger Taeniae, e. g. 

 T. solium, the dorsal longitudinal vessels are aborted. 



b. Uterus, in the unripe segment running as a straight tube from the pos- 



terior part of each segment to the anterior. In some Taeniae it is 

 transverse. Where the genital pores are double (right and left), the 

 uterus remains single, e. g. in T. elliptica. 



c. The albumen gland or vitellarium. In the small Taeniae the gland is 



saccular, in the larger tubular, and the tubes branched and anastomo- 

 sing. They contain small nucleate cells which break down into a 

 tenacious clear fluid. The gland is homologous with the bilaterally 

 symmetrical yolk gland or vitellarium of other Cestoda. Its duct 

 joins the ' fertilising ' canal at the spot where the latter is surrounded 

 by a mass of unicellular glands which make up the shell gland 

 indicated in this figure by a slight expansion above the albumen gland. 



d. Germ-glands, one on either side, composed of tubes much branched in 



the larger Taeniae. They contain clear uninucleate ova or germs. 

 The ducts unite in the middle line, and the common canal thus 

 formed unites with the fertilising canal which connects the spermatheca 

 to the uterus, before it is surrounded by the shell-gland. 



e. Testes appended in a racemose manner by very delicate ducts to the 



vasa deferentia. They occupy the ' dorsal ' surface of the segment, 

 whereas the female organs are confined to the ' ventral ' surface, and 

 were more abundant in the anterior half of the segment which is 

 removed, than in this, the posterior. 



f. Intromittent organ, essentially a specialization of the muscular ductus 



ejaculatorius. It is armed with spines in some Cestoda, which favour 

 its retention in the vagina of its own segment. It is here figured as 

 retracted and coiled up spirally. 



g. Vagina dilating into an oval receptaculum seminis or spermatheca, before 



joining the duct of the two germ-glands. It opens externally in the 

 posterior half of a saucer-like depression, the porus genitalis, on one side 

 of a segment, in the anterior half of which the male outlet is situated. 

 The generative outlets are similarly arranged in Taenia elliptica. 



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