448 RICHARD EVANS. 



to have seen iudividuals in which the interior is full of 

 plasraodial aggregations alone. He has also failed to distin- 

 guish between the yolk bodies and the nuclei of the flagel- 

 lated cells which have been taken in by the large amoeboid cells 

 in the same way as is described by Delage. But, on the other 

 hand, he has seen some of them decreasing in size and disap- 

 pearing, which Delage did not see, and consequently comes to 

 the conclusion that all the bodies figured in his large amoeboid 

 cells, which are the same as the '' poly nuclear groups ^^ of 

 Delage and the '^ plasmodial aggregations ^' of the present 

 memoir, are completely absorbed, a conclusion which is in no 

 way warranted. 



Moreover, the magnification to which he has drawn his figures 

 is not sufficiently high to enable him to distinguish between yolk 

 bodies on the one hand, and nuclei on the other. The figures, 

 therefore, which scarcely show any nuclear structure, save what 

 is sufficient to distinguish a vesicular nucleus as such, have no 

 value whatever for deciding such a point. These facts detract 

 considerably from the value of Noldeke's account, and cast a 

 doubt upon his conclusions. 



This brings to a close what we have to say as to the fate of 

 the flagellated cells, which, in our opinion, migrate into the 

 interior and become plastered to the surfaces of the cells with 

 vesicular nuclei. Ultimately, however, they break away from 

 these associations, and become the collar-cells of the young 

 sponge. 



B. The Differentiation, &c., of the Inner Mass. 



The views held with regard to the constitution and diff'eren- 

 tiation of the inner mass may be divided into two classes : 

 first, those according to which it consists of both " mesoderm" 

 and " endoderm," held by Ganin (4), and by Maas in his first 

 account (7); secondly, those according to which it contains 

 only an aggregation of cells called by some authors " endo- 

 derm," which is divisible, however, into several kinds of cells. 



