PHYLUM AND CLASS PORIFERA 123 



ductive cells. Certain of the flagellate cells then withdraw their 

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



Fio. 92.— Pheronema carpenter!, one nf the Hexactinellida. 

 (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 Coelenterates (Sect. IV). This is the 



