PROCEEDINGS OF SOCIETIES. 



195 



the anterior end is the trochal disc, a ciliated expanse vary- 

 ing in its structure ; at the anal end there is often a pair o£ 

 pincers ; there may be, however, no apendages at all. The 

 mouth leads into a proventriculus or gizzard provided with a 

 chitinous crushing apparatus ; the intestine which follows is 

 large but straight and simple. In Hydat'ma, a pair of glands 

 called by Ehrenberg " pancreas " open into the alimentary 

 canal. From the cloaca proceed two long tubes which coil 

 up the sides of the body, and each give off four delicate 

 branches terminating by ciliated trumpet-shaped organs 

 hanging freely in the perivisceral fluid. These form the 

 water- vascular system which is the great characteristic of the 

 Scolecida. The generative organs are simple enough, consist- 

 ing in the female of a simple ovary opening into the cloaca ; 

 in the male, which is much smaller than the female, and 

 destitute of alimentary apparatus, a testis and penis are 

 found. 



Lecture V. — The Scolecida include the following groups in 

 addition to the Rotifera, the Trematoidea, and Turbellaria, the 

 Cestoidea, and Acanthocephala, the Nematoidea and Gordia- 

 cea. The Trematods have no proper perivisceral cavity, that is 

 to say, instead of a corpusculated fluid, there is a cellular tissue. 

 The details of structure of Asjyidogaster were given (see 

 former lectures) . The existence of a germarium and of a 

 vitellarium was especially noticed — it being possible for the 

 impregnation of the ova to be effected before the accessory 

 yolk from the vitellarium was poured round it. The integu- 

 ment of Fasciola presents numerous lancet-like bodies of a 

 chitinous material, which aid it in progression, and call to mind 

 the bodies in the integument of some other Scolecida (fig. 4), 



The alimentary canal is in Trematods a blind sac, either 

 single or double, or, as in Fasciola, much branched. The 

 water-vascular system, essentially as in Aspidogaster, varies as 

 to the presence or absence of a pyriform sac. In the flukes 



