M. E. Mecznikow on the Rhabdocoela. 59 



communicating with the spinous apparatus; the spine itself is 

 connected with the poison-gland. 



Besides these two Prostomea I have met with Claparede's 

 Prostomum caledonicum* on Heligoland, and observed its sexual 

 organs. I have only to add to the accurate description of Cla- 

 parede 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. Schmardaf has found in the standing and brackish waters 

 of North America two Rhabdocoela 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 

 Acmostomese. 



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 difi'ers in form, and 

 in the absence of the marginal papillae, from the same organ of 

 the Acmostomese described by Schmarda. Behind this there are 

 two brown eyes, lying close upon the brain. The latter, which 

 is of the usual construction, gives oif two strong nervous stems 

 from each side. The animal observed has the sexes completely 

 separated ; but unfortunately I have only found a male indivi- 

 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 efi"erent 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, BuschJ 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 Annelides, Turbellaires, &c., pi. 5. fig. 5. 

 t Ncue wirbellose Thiere; Erste Halfte, p. 3, taf. 1. figs. 1, 2. 

 X Beobachtungen iiber wirbellose Thiere, p. 1 14, taf. 1 1 . fig. 9. 



