STRUCTURE OP THE LARVA OF SPONGILLA LACUSTRIS. 453 



rise to them. The method by which the cells come together 

 to form chambers corresponds to their origin from the flagel- 

 lated cells, and that by which the cells are derived from one 

 cell to the formation of the cell groups described above. It is, 

 therefore, highly probable that Noldeke has seen the formation 

 of flagellated chambers from the flagellated cells of the larvae, 

 as well as from the cell groups, the peculiar mode of origin of 

 which he did not recognise, and consequently classed them 

 along with the cells with granular nuclei as " Bildungszellen/' 



This brings to a close our remarks on the accounts already 

 published, and what most of all impresses us is their incomplete- 

 ness in every case. Ganin and Maas appear to have recognised 

 larvae belonging to type C alone — perhaps type B as well, — 

 while Gotte found types A, C, and D. But he seems to have 

 drawn type C as a larva, and described the metamorphosis of 

 type D. Delage was aware of the existence of types C and D, 

 but considered the former to be an abnormality, and believed 

 the latter to be the only one that pursued the normal course of 

 development ; while with regard to the former, so far as he 

 described it, he arrived at a quite erroneous conclusion with 

 regard to the origin and fate of the rings of cells occurring in 

 it. Gotte and Noldeke are the only two who were acquainted 

 with type A as a free-swimming larva. Noldeke, however, seems 

 to have completely missed the larva described in this memoir 

 as type D. The larva which I have described as type B seems 

 to be an entire stranger to the literature on the question. 

 However, it is one of the best examples possible of the value 

 of intermediate stages. It may be that Maas saw it, for he 

 draws amoeboid cells with yolk granules side by side with 

 incompletely divided cell groups. 



Now that the accounts already published have been compared 

 with that ofiFered in the present account, it is necessary to make 

 a brief summary of the points which are considered to have 

 been proved. 



