72 Proceedings of the Royid Society of Victoria. 



have become iiidi.stiuct in outline, and in place of one large 

 cell we have an ago-regation ot very many minute spherical 

 bodies, eacli with a dark spot in its centre, but each 

 aggregation still retains the form of the original amroboid 

 cell. In the same sections which exhibit this condition many 

 of the amceboid cells appear to have become rounded off, and 

 their contents have arranged themselves around a central 

 cavity, so that we have a hollow chamber lined by small 

 spherical cells. These chambers I believe to be the young* 

 flagellated chambers. They are certainly very different in 

 structure from the flagellated chambers of the adult sponge, 

 and only about half the size ; but this difference is readily 

 exj)lained by their embryonic condition. I have not been 

 able to trace the development of the chambers any further, 

 nor is it to be expected that the collars and flagella would be 

 developed before the young sponge was set free and required 

 them. 



Coincidently with the formation of the chambers in the 

 manner just descril)ed, a slit-like invagination appears on the 

 surface of tlie young sponge, and it is chiefly, if not solely, 

 around this invagination that chamber formation takes 

 place. This invagination I believe to be the commencement 

 of a communication between the chambers and the outside. 

 Unfortunately, I have only obtained a single embryo which 

 is sufficiently advanced to show the formation of the 

 flagellated chambers and the slit-liUe invagination, but I see 

 no good reason for doubting the normality of the ])henomena 

 above described. 



It thus appears that the flagellated chambers in 

 Stelospongus are formed by the breaking up of large 

 amoeboid cells, exactly as described by Mr. Carter in the 

 development of the gemmules oi' Spoiif/ilk'.. 



