FIG. 119. Development of Polygordius. After Fraipont. 



a. t Mother sperm cell ; ., c., sperm morulae ; */., spermatozoa. 



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

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

 7. formation of stomodaeum (st.\ and proctodaeum (fir.), which invaginate to meet 

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

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

 posterior segments ; u. form of adult Polygordius. 



