CHAPTER I. 

 PORIFEEA. 



Sponges reproduce by sexual and non-sexual means. To 

 the non-sexual kinds of reproduction belong — (1) sprotding 

 or huddmg, which may lead to the formation of complicated 

 stocks or colonies ; (2) the formation of small buds which 

 separate from the parent body and grow up independently 

 into new individuals ; (3) repi^oduction by means of 

 gemviida'. 



The investigations on the development of sponges from 

 the fertilized egg have not up to the present time yielded 

 a uniform plan for the embryology of this group, and they 

 frequently contradict one another. The following may be 

 mentioned as features common to the development of all 

 sponges. 



(1) The sexual products 

 arise in the connective 

 tissue of the so-called 

 mesoderm out of cells 

 which at first are not to 

 be distinguished from the 

 connective tissue cells of 

 this layer. 



(2) The eggs are not 

 surrounded by any cuti- 

 cular envelope (chorion) 

 or vitelline membrane. 

 They lie naked in a cavity 

 lined with endothelium 

 (Fig. 1 e) in the mesoderm of the parent body. Here the 

 expulsion of the polar globules, fertilization, and early de- 

 velopment take place. 



Fig. 1. — Egg of Placina trilopha in the 

 parent body (after MiGDEBüEG). r, polar 

 globules ; e, endothelial lining. 



