NOTES AND MEMORANDA. 287 



The apparent segmentation of the form leads the author to inquire 

 as to the possibility of his having had to do with a larval Annelid ; all 

 these forms, however, seem to agree in that they do not exhibit meta- 

 meric segmentation till a late period, and at any rate not until they 

 have developed setae at points corresponding to, and apparently indi- 

 cative of such segments ; while the presence of sexual products in the 

 forms observed militates against their being immature. Nor again 

 does the metamerism seem to be due to gemmation, nor is it the first 

 instance of such an arrangement; Busch recorded a case in 1851, the 

 characters of which w^ere in 1865 put by Metschnikoff in their true 

 light, while the Russian naturalist took this opportunity of recording 

 another example. The form appears to belong to the MicrostomecB. 



The most interesting points in a new species of Prostomium (P. 

 horeale) are the presence of a chitinous sabre-shaped spine, which is 

 placed to one side of the penis, and appears to be an organ either of 

 defence or oifence, and of a collection of glandular bodies of uncertain 

 function, set on either side of the base of the proboscis. In another 

 new species (P. fapillatum) Mereschkowsky observed the presence of 

 six papilliform projections at the anterior end of the body, which 

 serve undoubtedly as tactile organs. 



In a new species of Mesostomium, which he dedicates to L. Graff, 

 Mereschkowsky describes the presence of enlargements on the vessels, 

 which did not however exhibit either contraction or pulsation, and the 

 function of which remains obscure ; they do not seem to have been 

 hitherto observed in these forms. 



The author also makes some remarks on Dinophilus vorticoides, 

 Oscar Schmidt, and on the general Turbellaria-Fauna of the White 

 Sea. 



Digestive Organs of the Fresh-water Turbellarians. — Elias 

 Metschnikoff, who in 1866 was able to confirm the results of Claparede, 

 made three years earlier, as to the absence of an alimentary canal in 

 some of the Rhabdoccelous Planarians, returns to the subject,* and 

 points out that the results, which have been denied by Minot on a priori 

 grounds, have been confirmed by Uljanin (1870), Salensky (1872), 

 and much more lately by Graff. He further proceeds to consider how 

 far this character is one that is peculiar to these forms, and which so 

 impressed Uljanin as to lead him to give to them the name of Acoela, 

 or whether it is not rather one that is essentially common to the 

 whole of the Tm'bellaria. 



His account of the modes of digestion in a fresh-water Turbel- 

 larian allied to Mesostomium produdum, and in M. Ehrenbergii, is pecu- 

 liarly interesting. The former presented a fairly irregularly arranged 

 mass of digestive cells ; in these cells he found not only urinary concre- 

 tions, but other bodies which he feels compelled to regard as nutrient 

 particles ; in M. Ehrenbergii, which is transparent, he was able to 

 trace the history of these particles more completely. The chief food of 

 this worm is Nais prohoscidea, and an hour after ingestion he was 

 able to discover all the soft parts of the Nais in its enteric cells ; the 

 cuticle and its setae alone remained in the lumen of the tube. To 

 * 'Zool. Anzeiger,' i. (1878) 387. 



