AN INTRODUCTION TO ZOOLOGY 



other animals can be discussed successfully. The character of 

 the object to which sponges are attached causes them to assume 

 exceedingly irregular shapes, the rocks being frequently incrusted 



FIG. 74. Development of a simple sponge (Sycon raphanus). a, ovum; 

 b, c, ovum segmented ; d, blastula ; e, amphiblastula ; /, commencement 

 of invagination ; g, gastrula attached ; h, i, young sponge. (From 

 Parker and Haswell after Schulze.) 



