24 EMBRYOLOGY OF THE LOWER VERTEBRATES CH. 



eventually results a blastula (A 5) the upper portion of \vliich. 



forming rather less than a hemisphere, is composed of micromeres 



while the lower part is composed of large, richly yolked, macromeres. 



In Ainia the " oval"-sha prd egg measures about 2'5-3 mm. by 



Ki<;. 14. Segmentation in Acipenser (A), Ainia (B), and 

 Lepidotfau (0). (After Baslifnnl I , liynn-r. 



;ui. I Whitman.) 



A 1, 2 and 3, 15 I ami _', C 1 and '.'are \ii-ws .if th.- :i|.u-:il |...l-: the 

 remaining lignn'* an- M.lr \n-\\>. 



al.nut L^-2'5 mm. In tin- iv^ion of the aj.ical pole which li.-s at lln- 

 ml of lln- luii-j .1 hajH-il |Mi|-(.i<>ii riclirr in |n>l oplasin 



,ni ;i].|.K.ach in lact to a ^'Tininal disc; while lln- rest of lh- 

 [| i ich in dark g1 i-h l>n\\ n ylk. 



The segmentation i-'i-_ r . 11 I', begins, about ao IK.UI- and a hair 



