Ill 



POEIFEKA 



45 



Branched cells reminding ns of the mesenchyme cells of the larva 

 of Grantia. 



A 



- 



^^S- -o" T^^- "S." 5 - ^ 



Wt-A- 



y/ 



^lllljj,, B 



-^T^: 



9 



I \Wa 



\ -- r 



FIG. 22. Seven stages in the metamorphosis and fixation of the larva and growth 



of the young sponge of Plakina monolopha. (After Maas.) 



A, larva in amphiblastula stage ; granular cells budding off cells into interior. B, larva about to 

 fix itself. C, larva just fixing itself, flagellated half flat. D, fixed larva, flagellated cells beginning to 

 invaginate. E, " Rhagon " stage. F, G, two stages in subdivision of Rhagon cavity by downgrowth of 

 septa ; Jt, flagellated cells ; gr, granular cells ; men, " mesencliyme " ; s, septa dividing cavity of Kliagon. 



After fixation the flagellated cells collapse to form a solid mass, 

 which is speedily separated into smaller masses by ingrowths of the 



