v 
ic osssaanmas Beebe sesesestiniy 5 
Fic. 119.—Development of Polygordius.—After Fraipont. 
a., Mother sperm cell; 4., ¢., sperm morule; ¢., 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 stomodzeum (sz.), and proctodzeum (/7.), which invaginate to meet 
archenteron (ac.); 8. complete gut formed; 9. elongation of larva; af. sf., 
apical spot; céZ., ciliated ring; 2eph., primitive nephridia ; 10. formation of’ 
posterior segments ; 11. form of adult Polygordius. 
