SECTION III. —PHYLUM PORIFERA 



The Porifera, or sponges, belong to the lowest group of 

 the Metazoa. They live fixed to the surface of rocks, or to 

 submerged timber or seaweeds, so as to be incapable of 

 locomotion ; and have, in most cases, a general form which 

 suggests the vegetable rather than the animal kingdom. 

 But, in essentials, as will presently become 

 evident, the sponges are distinctly animal in 

 character, and the resemblances to plants 

 are entirely superficial. 



The majority of sponges are compli- 

 cated and difficult to understand, owing to 

 their elaborate mode of branching and the 

 fusion of the branches, and to the exceed- 

 ingly intricate character of the skeletal 

 parts, aside from their cellular structure. 

 Some, however, are free from these com- 

 plications ; and it is in one of these that 

 the main characteristics of sponges are 

 best studied. Such a simple form is Sycon, 

 a small sponge living attached to rocks on the seashore 

 towards or below low-water mark. Sycon gdatinosum Y has 

 the form of a tuft, one to three inches long, of branching 



1 This is an Australasian species, but the following account will apply in 

 all essential respects to Sycon ciliatum (Fig. 33) and S. clarkii of the coast 

 of New England. 



76 



Fjg. 33.— Sycon cili- 

 atum. 



(After Hyatt.) 

 Riverside Nat. His. 



