168 



AET. II. A. IZÜKA 



A) ; the second is accomplished about fourfcy minutes later (wood- 

 cut B) ; the third is completed about five hours and a half after 

 fertilization (woodcut C). 



A. 



li. 



Early stages of segmentation. 



A. Completed 2-cell stige seen from the lower pole. 140/1. 



B. Yiew from the ux^per pole after completed second cleavage. 140/1. 



C. „ „ ,, „ „ „ „ third cleavage. 140/1. 

 (Polar bodies are not indicated. All the figures were drawn from the living egg). 



Ciliated embryos first appear about 40 hours after fertiliza- 

 tion ; 4 or 5 hours after that the embryos are seen swimm- 

 ing about very active- 

 ly in the vessel. They 

 then show a marked 

 positive heliotactic nature, 

 so that the water in the 

 vessel may now be easily 

 changed by means of a 

 siphon. 



About 90 hours after 

 fertilization the setae be- 

 gin to appear. 



One of the embryos of 

 about 9 days age is 



An embryo 9 dfiys old, with 4 setigerous seg- 

 ments. 140/1. Xat. Size. 



represented in woodcut 



