STRUCTURE OF THE LARVA OF SPONGILLA LACUSTRIS. 451 



collar-cells. It is true that both classes are developed origi- 

 nally from cells with vesicular nuclei, but their mode of origin 

 is absolutely diflferent, as well as their fate. The " cell groups " 

 have been shown to be developed by the breaking up of one 

 cell, while the cells with granular nuclei increase in number by 

 the gradual transformation of the cells with vesicular nuclei. 



Delage divides the cells of the inner mass into three classes, 

 which must be compared with the similar classification I have 

 adopted above. Delage^s three classes are the following : — 

 "cellules epidermiques, cellules amceboides, et cellules inter- 

 mediaires;" while my three classes are termed "cells with 

 granular nuclei," "cells with vesicular nuclei/' and "cell 

 groups." The second class in each system is identical. There- 

 fore only the other two remain to be examined aud compared. 

 Since Delage considers the larva described by Maas, and in 

 the present memoir referred to as type C, to be an abnormal 

 form, he has probably not taken the class of cells described 

 above as cell groups into account, and has included what 

 there was of them in the larva which he considered normal, 

 which is type D of the present account, among his "cellules 

 intermediaires." As has been said already in describing the 

 larva type D, the cell groups are so few that probably they 

 would have been missed by me had I followed Delage in con- 

 sidering type D abnormal. 



It seems, therefore, that Delage's " cellules epidermiques et 

 cellules intermediaires " are equivalent to the class here termed 

 cells with granular nuclei, together with a few cell groups 

 which might have existed in his normal larvae, but which he 

 did not recognise. There is no valid reason for the division of 

 this class of cells into two. The " cellules intermediaires " 

 are separated from the " cellules epidermiques " for no other 

 reason than that their nuclei are slightly larger and their 

 situation deeper. The former statement, which is true only 

 of the cells lodged in the interior of the solid part of the 

 inner mass, and not of the cells which line the larval cavity, 

 and which are also included in this class, results from their 

 more recent origin from the cells with vesicular nuclei. How- 



