II 



FIG. 104. Development of Polygordius. After Fraipont. 



a., Mother sperm cell ; b. , c. , sperm morulae ; d. , spermatozoa. 



i. Ovum with large nucleus ; 2. two-cell stage; 3. four-cell stage; 4. blastosphere ; 

 5. gastrula ; ac., archenteron ; 6. closure of gastrula mouth or blastopore ; 

 7. formation of stomodaeum(^.), and proctodaeum(/r.), which invaginate to meet 

 archenteron (ac.) ; 8. complete gut formed; 9. elongation of larva; ap. sp., 

 apical spot ; ctl., ciliated ring ; neph., primitive nephridia ; 10. formation of 

 posterior segments ; ir. form of adult Polygordius. 



