PHYLUM AND CLASS PORIFERA 123 



ductive colls. Certain of the flagellate cells then withdraw their 

 flagella and pass into the internal cavity, becoming amoeboid. Soon 



Fio. 92.— Pheronema carpenteri, one of the Huxactinellida. 

 (From Wyville Thomson.) 



a large number of these amoeboid cells come to fill up a great part of 

 the cavity of the larva, which now passes into a stage corresponding 

 to the planula larva of the Ccelenterates (Sect. IV). This is the 



