50 ZOOLOGY. 



View of the Classification! of the Porifera. 



CaTnieospongios. 

 (Spongla.^ 



Calcisipongim. 

 (Sycou.) 



PORIFEKA. 



LaboraU/ry Work. — Sponges are difficult to preserve alive in aquaria 

 for study. Fine microscopic sections of the li\ing sponge may be made 

 "n-ith the razor or the microtome, and the tissues and eggs as well as the 

 young be studied, though, from their minuteness, the study of the 

 joung is very difficult. The ciliated young of Sycon cUiatum may be 

 obtained in the spring and summer by picking a portion of the sponge 

 to pieces and tearing out small fragments ^vith fine needles, until por- 

 tions are small enough to be examined under high ]K)wers of the micro- 

 scope. Researches on the finer structure and mode of growth of the 

 sponge are difficult, and require much skill and long training in his- 

 tological methods. The gross structure of sponges may be studied by 

 cross and longitudinal sections made with a razor or knife. 



