316 128 



differs from specimen to specimen, and in its rudimentary form it undergoes a change 

 of function. 



A fully developed alimentary canal we only find in the male of Rhinops vitrea 

 and in Notommata Werneckii. It is a question if really the male of Rhinops takes 

 food, at all events I have never been able to see an anus or a defecation; it is 

 further a very peculiar fact that the alimentary canal is very rudimentary in its 

 nearest allies, Hydatina and Notops brachionus, further that it is also lost in all the 

 primitive Rotifers, only excepting N. Wernecki and in all other freeswimming Rotifers. 

 With regard to N. Wernecki it is perhaps a question, if the mouth parts are not 

 mainly used to bite holes in the algæ; but having never seen this rare animal, I 

 have no opinion about this matter. 



In all other Rotifer males the alimentary canal does not function; a mouth 

 opening never exists, and also the mastax is absent. In the place where the alimentary 

 canal is to be found in the female, there is commonly a long broad band, which 

 with its posterior end embraces the testis and with the other is fastened to the hy- 

 podermic cells of the wheel-organ. This band in a few cases carries a peculiar bulk 

 like body in its anterior part immediately below the wheel-organ, in A. priodonta 

 it is of a remarkable form like a parrot's beak. In A. priodonta it is not always 

 present, at all events not equally developed; it is further found in the males of the 

 two Salpina species which I have seen; it contains no chitinous mouth parts, but 

 nevertheless I regard it as a rudimentary mastax. In a few cases we find two organs 

 on the side of the band which are regarded as rudimentarj^ gastral glands. Especially 

 in A. priodonta it looks as if the band contained vacuoles, but more thorough in- 

 vestigations on this point would be desirable. Also in the Sijnchœta males it looks 

 as if the band was hollow. In very many cases it is reduced to a simple band, 

 stretched out between the testis and the hypodermic cells below the wheel-organ; 

 even in this form it is by many authors, with whom I fully agree, regarded as a 

 remnant of the alimentary canal; but even this is whollj' wanting in the males of 

 many species. This for instance is the case with all the most reduced males, those 

 of Triarthra, Polyarthra, Pedalion, Conochilus, Pompholijx, Rattulus, but also of many 

 others which are not so much reduced f. i. G. hijptopus, G. stylifer. How sporadic and 

 capricious the occurrence of the rudiment of the alimentary canal really is, is best 

 seen in the Asplanchnas, where in A. priodonta, as mentioned above, it embraces the 

 testis and is stretched out like a long band through almost the whole animal; in 

 A. Briyhtwelli it has not been possible to find even the slightest trace of it, while in 

 A. Sieboldi a peculiar rodlike body stretched out from the corona and hanging free 

 in the body cavity can hardly be interpreted otherwise than as a rudiment of this 

 organ. Where it is in connection with the testis, it may be regarded as highly pro- 

 bable that it is here used as a means to keep the testis in place. 



The brain in the male as well as in the female lies dorsally over the ali- 

 mentary canal; it is commonly pear shaped, now and then a little bifid. I have the 

 impression that it is perhaps larger in the male than in the female sex but it is 



