366 RICHAED EVANS. 



the granules in the cells with vesicular nuclei to be purely 

 vitelline. 



The fourth observer to study the structure of the larva of 

 Spongilla and its metamorphosis was Yves Delage (1), who 

 wrote in the year 1893. 



Delage wisely discarded the terms which had been used by 

 all previous observers, and described the larva as consisting of 

 four kinds of cells, which he called flagellated or ciliated cells, 

 epidermal cells, amoeboid cells, and intermediate cells. 



The flagellated cells consist of the layer of cells which cover 

 the surface, and which pass into the interior, and are taken in 

 and ejected again by the amoeboid cells, finally becoming the 

 collar-cells of the chambers. 



The epidermal cells were described as forming a complete 

 layer of cells underlying the flagellated cells, which during 

 metamorphosis travel to the exterior, and give rise to the cells 

 of the flattened epithelium. 



The intermediate cells he described as being embedded in 

 the inner mass, and as forming a lining to the larval cavity. 

 They become the lining of the canals in the interior of the 

 sponge, in addition to giving rise to connective-tissue cells. 



The amoeboid cells are those which possess vesicular nuclei, 

 and which during the metamorphosis take in the flagellated 

 cells by a kind of phagocytic action, ejecting them again later 

 on. On being set free the flagellated cells become the collar- 

 cells of the chambers. 



Maas, who in the meantime had, from his studies upon other 

 siliceous sponges, arrived independently at embryological con- 

 clusions similar to those put forward by Delage, retracted in 

 1893 (8) his former statements with reference to Spongilla, 

 and recognised in the larva three kinds of cells, viz. the flagel- 

 lated cells, the amoeboid cells, and all the remaining cells. He 

 denied that the flagellated cells are taken in by the amoeboid 

 cells, and held that they become the collar-cells without passing 

 through the peculiar changes described by Delage. 



The last observer to study the development of Spongilla was 

 Noldeke (13), who wrote in the year 1895, 



