42 EXPLANATION OF FIGUlîRS. 



Explanation of Figures. 



AD the figures are drawn with a camera hioida. and are. unless otlier- 

 wise designated, magnified with Zeiss I) x 4. 



Reference letters used. 



a. anterior ])lastomerp. M mesomere-cell. 



<". egg. p. posterior hlastomere. 



ÏC. left l)ilat(n'aj cell. ph. polar body. 



in. mesomere-cell segmented. re. right l)ilateral cell. 

 The arrow under the ectomere-cell indicates its course of cleavage and 

 tJK' Roman numeral shows the order of the quartet to be formed. 

 Figs. 1~?)6 illustrate the development of Siphonnrla. 

 Figs. 37-00 illustrate tliat of Aplysia. 



