PLATE I. 



Fig. 1. — Transverse section through nephridium of adult. rV Ob. X4 0c. Camera. X 440. 



Fk;. 2. — Unsegmented egg with one polar body. (From life. ) J Ob. X 8 Oc. Camera. X 360. 



Fig. ■'!. — Two-cell stage, showing equal blastomeres. ( From life. ) £ Ob. X 8 Oc. Camera. X 360. 



Fig. 4. — Two-cell stage, showing unequal blastomeres. (From life. ) 5 Ob. X8 0c. Camera. X 360. 



Fig. 5. — Beginning of two-cell stage. (From life.) £ Ob. X8 0c. Camera. X 360. 



Fig. 6. — Section through two-cell stage. Chromosomes have lost their identity and granular vesicles have made 

 their appearance. Granular character of the yolk only shown in part of one blastomere. ,', Oil 

 Immersion. X 8 Oc. Camera. X 704. 



Fig. 7. — Beginning of four-cell stage. (From life.) J Ob. X 8 Oc. Camera. X 360. 



Fig. 8. — Four-cell stage, showing polar furrow. (From life.) ,} Ob. X 8 Oc. Camera. X 360. 



Fig. 8a. — Section through four-cell stage, showing granular vesicles which make their appearance after the dis- 

 appearance of the chromosomes. ,' 2 Oil Immersion. X8 0c. Camera. X 704. 



Fig. 9. — Four-cell stage passing into eighth-cell stage. Seen from above and showing the twisting of the blasto- 

 meres. I Ob. X 8 Oc. Camera. X 360. 



Fig. 10. — Eight-cell stage, showing rotation of blastomeres. (From life.) | Ob. X8 0c. Camera. X360. 



Fig. 1 1. — Section of eight-cell stage ready for sixteen-cell stage. Position of mitotic figures indicate meridional divi- 

 sion, y'j Oil Immersion. X 8 Oc. Camera. X 704. 



Fig. 12. — Young blastula showing "blastoccele pore." (From life.) ,\ Ob. x 8 Oc. Camera. X360. 



Fig. 13. —Section through young blastula showing blastocrele pore. rV Oil Immersion. X8 0c. Camera. X 704. 

 116 



