452 EICHARD EVANS. 



everj great credit is due to Delage for showing that the flagel- 

 lated cells of the larva became the collar-cells of the young 

 sponge, though he is in error in denying that they may also be 

 developed from the cells of the inner mass ; and the division 

 of the class of cells with granular nuclei into two is, to say 

 the least, needless. 



The last account to be considered is that of Noldeke (11), 

 who derives the whole sponge, like Gotte, from the inner mass. 

 Noldeke describes the inner mass as ^^endoderm," and dis- 

 tinguislies between endoderm cavity and endoderm nucleus. 

 The latter varies according to the age of the larva. In 

 the youngest larvse, which correspond to type A of the 

 present account, the endoderm nucleus consists of large cells 

 which contain several food granules. In older larvse differen- 

 tiation has set in, so that the inner mass consists of 

 " Bildungszellen " and " Amoeboidzellen," ihejormev class 

 being equivalent to the two classes described in the present 

 memoir as cells with granular nuclei and cell groups, the latter 

 class being equivalent to the class of cells here described as 

 cells with vesicular nuclei. The most important error in this 

 grouping of the cells is the classifying together of the cells 

 with granular nuclei and the cell groups. We may repeat, in 

 fact, the remark made in reviewing Gotte's work; their mode 

 of origin is different as well as their ultimate fate. Con- 

 sequently they cannot belong to the same class. 



Noldeke says there are two methods by which the flagellated 

 chamber originates: first, from one mother cell by division; 

 secondly, by the coming together or migration of many distinct 

 cells to one spot. These two statements are highly suggestive. 

 If the flagellated chambers were derived from cells of the inner 

 mass alone we would hardly expect to find these two methods of 

 origin occurring side by side. But if the flagellated chambers 

 are derived on the one hand from flagellated cells, and on the 

 other hand from the cell groups, as has been shown in this 

 paper to be the case, we would almost expect to find that they 

 were formed in two different ways. Noldeke's two methods 

 evidently correspond to the two kinds of cells whicli give 



