Miscellaneous. 333 



supposed vibratile ampulloo, figured by M, Maas in a larva still 

 having all its periplieral cylindrical cells in place, are nothing but 

 common rounded laounse ; their limiting cells have no cilia and in 

 no way arise from the layer which clothes the cavity of the larva. 



The pores and the oscula are distinct from their origin, the latter 

 being upon the middle convex portion of the young sponge, while 

 the former, which are much more numerou';, are situated at the 

 boundary between the convex body and the peripheral membrane, 

 or upon this membrane itself. 



In the foregoing paragraphs I have indicated only the general 

 course of the embryogcny. I shall explain shortly how these pheno- 

 mena are complicated by the division of cells and other details. 



In Ai/hjsilla, which is a fibrous sponge, the formation of the 

 ectoderm and of the ampulla; is similar, almost to the details, to that 

 which has just been described for Sponcjilla. Just as in Spongilla, 

 the mesodermic amoeboid cell is cast off at the periphery and remains 

 in the parenchyma outside the ampulloe, while in Espcrella it remains 

 for a long time in the interior of the ampulla, of the formation of 

 which it has been the centre. 



These now observations will be understood as modifying in a 

 certain degree the interpretation which I put forward last year on 

 the subject of the formation of the ampullar in this latter type. 



To conclude : the ectoderm arises at the expense of cells primi- 

 tively internal ; the ciliated cells take no part in its formation ; 

 they pass into the interior of the body, are captured by mesodermic 

 amoeboid cells, and later on regain their liberty and take part in the 

 formation of the ampullar and canals. This capture of the ciliated 

 cells is, after all, nothing but a phenomenon of phagocytosis, which is 

 incomplete in that it is temporary. This terra is the more applic- 

 able, since a certain number appear to be really digested. It is 

 probable that at the moment when they lose their cilia these cells 

 undergo a temporary diminution of their vitality, and that the 

 amoeboid cells, working on their own account, capture them as they 

 Avould food-matter, but do not succeed in digesting them. It is 

 very curious to see an incident of this kind becoming a normal 

 phenomenon of the development. There is something in it which 

 recalls the phenomena of histolysis described by Kovalevsky in the 

 Insects, but with this great difference, that here the elements 

 incoi-porated by the phagocytes are utilized in the subsequent histo- 

 geny directly, and not as simple nutritive matter. — ComiJtes Itendus, 

 tome cxiii. no. 5 (3 aout, 1891), pp. 267-2G9. 



On the Devthimient of the Blastodermic Layers in Isopod Crustacea 

 (Porcellio scaber). iJy M. Louis Houle. 



In a former note I have ex])lained the origin of rhe blastoderm 

 in the embryos of Porcellio. The germinal disk, containing the 

 nucleus of the oosperm, envelops the nutritive yolk, borrowing 

 therefrom the necessary protoplasm for this extension ; its nucleus 

 divides, by the usual process of karyokinesis, into several segments, 

 which again undergo division ; and the whole is thus converted into 

 cells, which rapidly increase in number. On the completion of this 



