Chap. 22 



SPONGES A SIDE LINE OF EVOLUTION 



455 



Fig. 22.1. A cluster of common calcareous sponges that grew hanging from a 

 harbor wharf pile. The loosely branched one is Leucosolenia, each branch an in- 

 dividual sponge. The others are: (left) the crowned sponge, Sycon (Grantia), its 

 long fingers with crowned tips; and (top) a shapeless bread-crumb sponge, Hali- 

 chondria. (Photograph of living sponges by Douglas P. Wilson, Marine Biological 

 Laboratory, Plymouth, England.) 



yet in favorable conditions they will come together and become perfectly reor- 

 ganized into their former shape (Fig. 22.9). 



Sponges are undoubtedly multicellular animals. But in very ancient times 

 they drew away from the developments going on in other multicellular ani- 

 mals. In their early history they must have adopted a static existence, thor- 



