452 SCIENCE PROGRESS. 



the actual transformations of the cihated cells . . . into the 

 flattened epidermis . . . are . . . meagre " (yes, indeed !), 

 and again admits on the same page " the immigration into 

 the interior of a part of the ciliated cells ". P^or all these 

 reasons it seems to me not only justifiable but even neces- 

 sary to regard Wilson as a supporter, in spite of himself, 

 of the view that the layers become reversed during the 

 metamorphosis. Wilson's memoir seems, in fact, to have 

 been born out of due season, so to speak ; an anachronism, as 

 Maas has well termed it. Commenced, and apparently for the 

 most part written, at a time when the inversion of the layers 

 was not for a moment suspected, when Metschnikoff's almost 

 prophetic statements (1874) had been forgotten apparently 

 even by their author, Wilson's work came forth in an epoch 

 in which the stand-point which it represented had already 

 been clearly shown to be impossible, and the views it put 

 forth were antiquated before they were published. 



Noldeke (1S94) on the other hand, sees the facts of 

 sponge development in a very different light. In the larva 

 of Spongilla he has described in a most convincing manner 

 the way in which the ciliated layer becomes broken up and 

 carried into the interior after fixation. But with regard to 

 the ultimate fate of these ciliated cells, Noldeke's views are 

 original and peculiar. He believes with Delage that the 

 amoeboid cells of the inner mass capture the ciliated cells 

 and engulf them, in a manner analogous to phagocytosis 

 (see Science Progress, May, 1894). But whereas Delage 

 believes that the cells so captured are set free again to form 

 the chambers, Noldeke is of opinion that they are com- 

 pletely absorbed and digested by the phagocytic amoeboid 

 cells. In other words he agrees with Goette, whose 

 views have been quoted above, to the extent of believing 

 the external ciliated layer of the larva to be lost, though 

 not thrown oft", during the metamorphosis, so that the 

 whole sponge is built up from the inner mass alone. In 

 this mass epidermic cells, amoeboid cells and formative cells 

 (Bildungszellen) are to be distinguished. The chambers 

 are stated to arise from the latter, either by division up of 

 a single cell, or by a coming together of cells from different 



