M. E. Mecznikow on the Rhabdocoela. 61 



that which is described as such by previous observers perhaps 

 only a torn place produced by division ? 



On the two sides of the body there are two very fine water- 

 vascular stems (fig. 6 r.c), the opening of which, however, I 

 could not find. 



The Alaurina observed by me is evidently not a larva, but 

 rather furnished with hermaphrodite sexual organs, which are 

 present in each "segment," and sometimes even occur in double 

 number in one or more of the segments. The testes are nume- 

 rous and distributed in the body (fig. Qt), appearing like cap- 

 sules containing the zoospermia. The male apparatus also in- 

 cludes a seminal vesicle of considerable size {v. s.), the eflferent 

 duct of which opens into a tubular penis [pe.) composed of 

 chitine. The extremity of this is inserted into the male genital 

 orifice, which is situated on the side of the body and often sur- 

 rounded by a cutaneous projection. 



Near each seminal vesicle there occurs an ovum furnished 

 with a nucleus and nucleolus, which forms the female apparatus. 

 I could not find the female genital aperture; but, as it can 

 hardly be wanting (for the male orifice is too narrow to furnish 

 room for both male organs during copulation), I am inclined to 

 think that it is only present at the time of copulation. 



As I have now described some of the peculiarities of organiza- 

 tion of the animal observed, I may be allowed to draw one or 

 two conclusions therefrom. In the first place, I must assert that 

 the parts of which the body is composed are by no means buds 

 which would subsequently separate. This opinion is founded 

 upon the fact that the whole animal possesses a common pro- 

 boscis, mouth, and intestinal canal, as well as common aqui- 

 ferous vessels ; and I have never seen traces of these parts upon 

 the segments when already sexually mature. Perhaps, however, 

 the parts above interpreted as segments are to be regarded as 

 the joints of an animal colony analogous to the Cestoda, as was 

 urged upon me by Prof. Leuckart (who also first called my at- 

 tention to the similarity of my Turbellarian to Busch's Alau- 

 rina) . 



As regards the systematic position of this worm, which I de- 

 nominate Alaurina composita, I think that, . together with the 

 animals observed by Busch and Claparede, it forms a distinct 

 family in the neighbourhood of the Microstomea, to which the 

 Alaurina are more or less related from the resemblance in the 

 structure of the sexual organs and intestine. 



If my statements are correct. Max Schnitzels system cannot 

 remain quite unaltered, inasmuch as he describes the Microsto- 

 mea as Arhynchia, which, however, will not do for the Alaurina 

 which are furnished with a proboscis. Perhaps the Microstomece 



