PHYLUM PORIFERA 



IOl 



Histology. — The sponges are among the simplest of the 

 Metazoa with regard to the differentiation of their cells, but 

 they seem quite complex when compared with the Protozoa. 



. . ,~x J* 



A 



Fig. 60. — Types of sponge spicules. 

 a, b, monaxon; c, d, tetraxon; e, triaxon; 

 f, polyaxon. (From the Cambridge 

 Natural History.) 



Fig. 6i. — Piece of net- 

 work of horny fibers from 

 the bath sponge, Euspongia. 

 (From Sedgwick.) 



The cells of sponges may be separated into three groups: 

 (i) those of the dermal layer, (2) those of the gastral layer, and 

 (3) the ameboid cells in the jelly between the dermal and gastral 

 layers. The classes of cells and the layers to which they belong 

 are shown in Table III. 



TABLE III 



CLASSES OF CELLS FOUND IN SPONGES 



A. Dermal 

 Layer 



B. Gastral 

 Layer 



C. Middle Re- 

 gion 



