M. KE. Mecznikow on the Rhabdoccela. 59 
communicating with the spinous apparatus; the spine itself is 
connected with the poison-gland. 
Besides these two Prostomee I have met with Claparéde’s 
Prostomum caledonicum* on Heligoland, and observed its sexual 
organs. I have only to add to the accurate description of Cla- 
paréde that the animal does not, as described, possess one seminal 
vesicle, but three of them (fig. 4:v.s.), of which two are situated 
upon the upper surface of the penis and the third near its point 
of aperture. I must also remark that these vesicles are not 
imbedded in the interior of the sheath of the penis, but outside 
of it. 
II. Schmarda+ has found in the standing and brackish waters 
of North America two Rhabdoccela with a terminal pharynx 
and eyes placed behind it (that is to say, with the characters of 
the genus Prostomum, according to former notions, when the 
proboscis was regarded as the pharynx) ; of this he has formed 
a distinct genus, Acmostomum, the representative of the family 
Acmostomez. 
I found a marine species of this family on Heligoland. This 
pale-brown species, which measures 1°5 millim. (fig. 5), possesses 
at the anterior end a conical pharynx, which differs in form, and 
in the absence of the marginal papilla, from the same organ of 
the Acmostomez described by Schmarda. Behind this there are 
two brown eyes, lying close upon the brain. The latter, which 
is of the usual construction, gives off two strong nervous stems 
from each side. The animal observed has the sexes completely 
separated; but unfortunately I have only found a male mdivi- 
dual, the generative organs of which consist of several testes 
constructed exactly as in Monocelis (fig. 5 r. s.), and of a strong 
seminal vesicle (v. s.) furnished with a muscular efferent duct. 
The zoospermia with which the vesicle was filled are represented 
in fig. 5 a. 
The species just described may very well be regarded as the 
representative of a peculiar genus ; but I leave it for the present 
in the still imperfectly known genus Acmostomum, under the 
name of A. dioicum. 
III. Under the name of Alaurina prolifera, Busch} has de- 
scribed an animal found by him only on one occasion, at Malaga, 
upon the systematic position of which he was in doubt. It was 
an elongated animal, with cilia and stiff hairs, and was met with 
in process of transverse division. 
A Turbellarian larva, with its caudal extremity apparently 
presenting indications of a segmentation, described and figured 
* Recherches sur les Annélides, Turbellaires, &c., pl. 5. fig. 5. 
+ Neue wirbellose Thiere; Erste Hialfte, p. 3, taf. 1. figs. 1, 2. 
{ Beobachtungen iiber wirbellose Thiere, p. 114, taf. 11. fig. 9. 
