ENTOZOA. 



87 



39 



the eversion of the intromittent organ and the exclusion of the eggs. 

 Two accessory vesicles communicate with the common generative 

 passage, one of which is probably a sperm-reservoir, the other a 

 nidamental sac ; the ova of some species are attached by short 

 filaments, the secretion of such a sac, to the stems of aquatic plants. 

 The chief modifications of the generative organ in the parasitic 

 Trematoda will be understood by reference to tlie description of 

 them already given in the two species infesting the human subject. 

 A third modification may be briefly noticed as it exists in the 

 Distoma perlatum, discovered by Nordmann in the intestines of the 



Tench. It is illustrated in the sub- 

 joined cut from the magnified figure, 

 given in that excellent observer's beauti- 

 ful work. * \nfig. 39. i, is the vagina 

 expanding into A, the glandular uterus, 

 or nidamental organ ; /, m, are the two 

 testes, beset internally with small spines; 

 «, the prominent tube, by which the 

 ova are excluded; o is the termination 

 of the oviduct in the cavity of the tes- 

 tis m ; p, p, are the convolutions of the 

 oviduct, laden with ova, received by r, 

 the short tubes leading from the ova- 

 ria q, q, which are widely extended 

 through the parenchyme of the sides of 

 the body. 



As to the development of the TVe- 

 matoda. When the Entozoologist 

 contemplated the Tcenia fixed to the 

 intestine, with its uncinated and suc- 

 torious head buried in the mucous 

 membrane, rooted to the spot, and im- 

 bibing nourishment like a plant ; — 

 when he saw the sluggish Dw^owa adher- 

 ing by its sucker to the serous membrane of a closed internal cavity ; 

 — he naturally asked himself how they got there? And finding 

 no obvious solution to the difficulty of the transit on the part of such 

 animals, he was driven to the hypothesis of spontaneous generation 

 to solve the difficulty. It is no wonder that Rudolphi and Bremser, 

 who studied the Entozoa rather as Naturalists than Physiologists, 

 should have been led to apply to them the easy explanation which 

 Aristotle had given for the coming into being of all kinds of Vermes, 



♦ LXXn. p. 91. t. ix. fig. 4. 

 o 4 



Distoma perlatum. 



