112 ZOOLOGY. 
of the crystals of oxalate of lime in the urinary tubes of 
many insects and the concretions of phosphate of lime in 
the organ of Bojanus of Lamellibranch mollusks.* The 
canals terminate in a small pulsating vesicle and pore, as in 
the Trematodes. 
The Cestodes are hermaphroditic, and each of the body- 
segments except those nearest the head contains male and 
female reproductive organs. ‘The male parts consist, as in 
the Trematodes, of testes, vasa deferentia, and a muscular 
sac With acirrus or intromittent organ, which may penetrate 
the vagina of the same segment. The female organs consist 
of an ovary (germigene), yolk-stock (vitellogene), uterus or 
matrix, receptaculum seminis, and vagina, the latter opening 
by a pore situated in Tenia (Fig. 77) on the side, or in 
Bothriocephalus on the ventral surface of the segment. 
There is a great deal of variation in the reproductive organs 
of the tape-worms; a general idea of the relations of parts 
may be obtained by reference to Figs. 77 and 79 The 
ovary forms the most important part. It is much devel- 
oped and very complicated in structure. As Gegenbaur 
states : ‘‘ The preservation of the species is here subject to 
innumerable difficulties, owing to the animal living in dif- 
ferent hosts at different stages of development, and to the 
wanderings which this mode of life entails ; consequently a 
large number of ova have to be produced, and the cer- 
tainty of fecundation insured.’? (Elements of Comparative 
Anatomy, second edition, English translation.) The 
male organs and products are first developed, and the 
receptaculum seminis stored with spermatic cells before the 
eggs fully develop in the ovary, and all these parts develop 
earliest in the terminal segments of the body destined to 
form the proglottides. 
Development begins very probably, as in the Trematodes, 
* This is Leuckart’s opinion. Sommer and Landois claim that these 
bodies are scattered through the substance of the body, and do not 
occur in water-vessels, Huxley endorses this view. But if these bodies 
are concretions and the water-vessels are mainly excretory, as they cer- 
tainly appear to be, we should judge that Leuckart’s view was the bet- 
ter grounded. 
