100 ANIMAL PAEAS1TES. 



twisted stem, J'" in length. d. The seminal ducts, placed on the 

 dorsal side of the capsule of the uterus in the interspace between 

 the lateral horns, are ' ^'" in thickness, but have no per- 

 ceptible connection with the vesicle of the penis or the testes. 

 e. The testes, according to Eschricht, are a layer of white 

 granules (0*030 O'OSO'"), placed in a corresponding network, 

 and containing in their interior, fine, spiral filaments (sper- 

 matozoid capsules). 



B. Ova and*Embryos. 



The ova, of which we have already spoken in the definition of 

 the species, exhibit an external hard, brittle shell, which is only 

 broken up by a very strong pressure into polygonal fragments 

 with sharp edges, but frequently breaks in such a way that they 

 represent operculated ova, exactly like those of the Trematoda. 

 If MM. Seeger-Wundt only describe the former, they cannot 

 have made an independent examination. With a little practice, 

 especially with the employment of caustic potash, we may easily 

 discover the degree of pressure necessary to cause the operculum 

 to open. From the opercular opening a limpid vesicle then 

 emerges, in which, however, I have not yet found the six 

 booklets, probably from want of skill. 



Although Von Siebold allows these booklets to possess a 

 similarity with the hooks in the circlets of the Tcenice, it is 

 certainly going too far to expect to find in these resemblances or 

 differences such as are seen in the mature species. It is, how- 

 ever, a question whether at least a part of the eggs of the 

 Bothriocephali are not produced with undeveloped embryos, so 

 that the latter are only perfectly formed free in nature, as in the 

 eggs of the Ascarides. The mechanism of the immigration of 

 the embryos, if they are really furnished with six booklets, will 

 be found in the Introduction. 



Resting scolex. In order to trace this gradually in its course, 

 it is undoubtedly most advisable to explain exactly the behaviour 

 of these organisms when we meet with them in other parts of the 

 animal kingdom. In the intestines of fishes, especially marine 

 fishes, certain cestode worms live, which are furnished with a 

 band-like, inarticulate appendage, but still exhibit no commence- 

 ment of sexual development, and which, as was first ascertained 

 by Creplin, and as we have already mentioned, become converted 



