FRESH-WATER SPONGES. 



123 



clear streams and ponds, is difficult to transfer to 

 the aquarium without damage. It has been effected, 

 however, and Mr. F. Meggy gave a description in 



Fig. 83. 



Spicules of Spongilla fluvia tilts. 



an eany volume of ' Science Gossip/ of a successful 

 experiment in acclimatising this animal. If only 

 domesticated its development becomes one of the 

 most interesting of microscopical investigations. The 

 young are seen thrown off as gemmules, and the 

 greenish-yellow gelatinous flesh, which constitutes the 

 true sponge, is seen investing the spicules or rather, 

 the latter are imbedded in the sarcode or flesh. The 

 shapes of these spicules are due to an organic crystal- 

 lisation, and although admirably symmetrical in form, 



