CHAPTEE IX 



« 



POEIFERA {continued) : EEPEODUCTION, SEXUAL AND ASEXUAL- 

 PHYSIOLOGY DISTRIBUTION FLINTS 



The reproductive processes of Sponges are of such great import- 

 ance in leading us to a true conception of the nature of a sponge 

 that we propose to treat them here in a special section. Both 

 sexual and asexual methods are common ; the multiplication of 

 oscula we do not regard as an act of reproduction (p. 174). 



Fig. 111. — A, amphiblastula larva of Sycon raphanus ; B, later stage, showing invagina- 

 tion of the flagellated cells, c.s, Segmentation cavity ; ec, ectoderm ; en, endoderm. 

 (After F. E. Schiilze, from Balfour.) 



A cursory glance at a collection of sponge larvae from 

 different groups would suggest the 'conclusion that they are 

 divisible into two wholly distinct types. One of these is the 

 amphiblastula, and the other the parenchymula. This was the 

 conclusion accepted by zoologists not long ago. We are indebted 

 to Delage, Maas, and Minchin for dispelling it, and showing that 



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