632 WILSON. 



PLATE XXXV. 

 [Fig. 77 to 95, from life ; the others from preparations ; 270 diameters.] 



Figs. 77 to 81. Cleavage of an isolated ^ blastomere up to the 8-celled stage, 

 observed in one position. Fig. 78 shows the nearest approach to the spherical 

 form. Identical with normal form of cleavage. 



Figs. 82 to 86. Cleavage of ^Ij^ embryo (a pair of blastomeres from 4-celled 

 stage). Slight inequality in the 4-celled stage. Fig. 85 represents another speci- 

 men showing perfect equality in the 4-celled stage. 



Figs. 87 to 91. Cleavage of isolated X blastomere, exactly corresponding 

 with that of the % blastomere shown in Figs. 77-81. 



Fig. 92. Unequal 4-celle.d stage of ^ blastomere ; cf. Fig. 90. 



Fig. 93. The same individual as Fig. 91 ; i6-celled stage. A large cleavage- 

 pore on the lower side. 



Fig. 94. Another specimen like the last (i6-celled stage, )i embryo), followed 

 from the beginning ; the 4-celled stage was equal. 



Fig. 95. The same specimen later ; 32-celled stage. Large cleavage-pore on 

 the lower side. 



Fig. 96. Another specimen (32-celIed ^ embryo). Cleavage-pore very small. 



Fig. 97. i6-celled stage from isolated ^ blastomere, from the side. 



Fig. 98. The same, nearly from lower pole. No cleavage-pore. 



Fig. 99. From isolated y^ blastomere. Transition from 16 to 32-celled stage. 

 From lower pole. No pore. Bilaterality slightly indicated. 



Fig. 100. From isolated y^ blastomere ; 32 to 64-celled stage. Attached to 

 it is a blastula of about )/% the normal size (± 24 cells). No membrane. 



Fig. ioi. Unilateral development. Half-sized 4-celled stage (equal), attached 

 to the other undivided y^ blastomere. Membrane intact. 



Fig. 102. Unilateral development. Half-sized blastula (± 128 cells), with 

 undivided l^ blastomere. Membrane intact. 



