SPONGES 



77 



non-ciliated dermal layer (Fig. 60, /), the cells of which may form 

 precocious spicules, so that both the metamorphosis and the histo- 

 genesis may be said to begin before fixation and during the larval 



period. If we compare this larva with that of Leucosolenia, as de- 

 scribed above, we see that it differs from it only in the fact that 

 the germ layer formation is thrown back, so to speak, from the 

 larval to the embryonic period, so that the Sycon amphiblastula 



