M. BE. Mecznikow on the Rhabdoceela. 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 7.a.), 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. 6 ¢), appearing like cap- 
sules containing the zoospermia. The male apparatus also in- 
cludes a seminal vesicle of considerable size (v. s.), the efferent 
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 1s 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 [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, | think that, together with the 
animals observed by Busch and Claparéde, it forms a distinct 
family in the neighbourhood of the Microstomee, to which the 
Alaurine are more or less related from the resemblance in the 
structure of the sexual organs and intestine. 
If my statements are correct, Max Schultze’s system cannot 
remain quite unaltered, inasmuch as he describes the Microsto- 
mee as Arhynchia, which, however, will not do for the Alaurine 
which are furnished with a proboscis. Perhaps the Microstomee 
