PLATE I. 



Fig. 1. Transverse section through nephridium of adult, fa Ob. X 4 Or. Camera. X440. 



Fig. l\ Unsegmented egg with one polar body. (From life.) ! Oh. X 8 Oc. Camera. X 360. 



Fig. 3. Two-cell stage, showing equal blastomeres. (From life. ) J Ob. X8 0c. Camera. X360. 



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



Fig. 5. Beginning of two-cell stage. (From life. ) 5 Ob. X 8 Oc. Camera. X360. 



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. fa Oil 

 Immersion. > 8 0c. Camera. 704. 



Fig. 7. Beginning of four-cell stage. (From life.) I Ob. X8 0c. Camera. X 860. 



Fig. 8. Four-cell stage, showing polar furrow. (From life.) 'Ob. X 8 Oc. Camera. X360. 



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

 appearance of the chromosomes, j'j Oil Immersion. X 8 Oc. 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.) I Ob. X 8 Oc. Camera. X 360. 



FlG. 11, Section of eight-cell stage ready for sixteen-cell stage. Position of mitotic figures indicate meridional divi- 

 sion, fa Oil Immersion. XSOe. Camera. X 7(14. 



Fig. 12. Young blastula showing "blastocrele pore." (From life.) 5 Ob. X 8 Oc. Camera. X360. 



Fig. 13. Section through young blastula showing blastoccele pore. iV Oil Immersion. X 8 Oc. Camera. X 704. 

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