154 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 defer entia, and a muscular 

 sac with a cirrus 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 Tcenia (Fig. 107) on the side, or in 

 BothriocepJialus 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. 107 and 109. 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. 



