Fig. 89. — Development of Polygordias, — After Fraipont. 



a., Mother sperm cell ; b., c, sperm morulas ; d. t spermatozoa. 



1. 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 stomodasum (st.\ and proctodaeum (pr.) f which invaginate to meet 

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

 spot; ciL, ciliated ring; nepk., primitive nephridia ; 10. formation of posterior 

 segments; n. form of adult Polygordius. 



