480 On the Development and Minute Anatomy of the Infusoria. 



space, and the half of the original germ-nucleus, which often 

 remains clearly connected with the other half. " This appear- 

 ance cannot be reconciled with the idea of a defined intestinal 

 canal running circularly through the body of the Vorticella and 

 beset with stalked stomach-vesicles ; for since the posterior half 

 of the body, before the commencement of the diagonal fission, 

 showed just as numerous nutritive masses (stomach-vesicles) as 

 the anterior, it is clear that this half must have contained a seg- 

 ment of the intestinal canal. By the cleft along the line of fission, 

 the intestinal canal, like the germ-nucleus, must have been cut 

 through in two places, and then it would have been impossible 

 for the anterior half of the animal to go on taking nourishment ; 

 but there must have been a time of rest, during which a new uni- 

 ting segment must have been developed between the two widely 

 separated portions of the intestine." 



Prof. Stein proposes the following revision of the Vorticellince 

 (Ehr.) ; the Stentors to be excluded, as they are ciliated over their 

 whole surface. 



Vorticellince. 



1. Stalkless, free swimmers: Trichodina, Urocentrum. 



2. Stalked; stalk contractile : Vorticella, Carchesium, Zootham- 

 nium. 



3. Imbedded in a common gelatinous investment : Ophrydium. 



4. Inclosed in a cup-shaped cell : Vaginicola, Cothurnia, Mitim- 

 nus, Lagenophrys. 



5. Provided with a non-contractile stalk : Epistylis, Opercularia. 



6. Wliolly non-contractile bodies : Spirochona. 



Of these, he says, that he has evidence that Vorticella, Vagi- 

 nicola, Cothurnia, Epistylis, and Opercularia possess distinct Aci- 

 neta-forms. 



EXPLANATION OF PLATE XVI. D. 



Fig. 1. Full-grown encysted Vorticella microstoma : a, the retracted oral 

 circlet of cilia ; b, the nucleus ; c, the contractile space. 



Fig. 2. A cyst separated from its stalk. 



Fig. 3. The same more advanced. The nucleus has broken up into spore- 

 like globules. 



Fig. 4. The same still more developed. The mother-cyst or original body 

 of the Vorticella, d, has become sacculated, and many clear spaces 

 have appeared in it. 



Fig. 5. One of the sacculations of the mother-cyst has burst through the 

 envelope and has given exit to the gelatinous mass e containing 

 the spores. 



Fig. 6. Acineta-form of Vorticella microstoma, which has arisen from a 

 cyst similar to fig. 2 : b, nucleus. 



Fig. 7. The stalked Acineta-form of V. microstoma, until now described as 

 Podophrysfixa : /, the young Vorticella, the result of the trans- 

 formation of the nucleus of the parent. 



Fig. 8. The young, free Vorticella : a, b, c, as in fig. 1 ; g, posterior circlet 

 of cilia. 



