636 WILSON. 



PLATE XXXVII. 



[Figs. 121 to 123, 126 to 130, from life ; the others from preparations. 270 diameters.] 



Fig. 115. Double 4-celled stage. Nearly equal type. 



Fig. 116. Transition from double 8-celled to double i6-celled stages, obliquely 

 from lower pole of each twin. Both of the unequal type. The axes form an 

 acute angle. 



Fig. 117. Double 8-celled form, preparing for division. Both of the unequal 

 type. The axes at right angles. 



Fig. 118. Double 8-celled stage. 



Fig. 119. Double 8-celled form, preparing for division ; unequal type. 



Fig. 120. Double blastula, 3)^ hours. 



Fig. 121. Four-celled form, from isolated micromere of 8-celled stage. 



Fig. 122. Succeeding 8-celled stage (from another but similar specimen). 



Fig. 123. Succeeding i6-celled stage of the same individual ; upper pole. 



Fig. 124. A similar form from the lower pole. 



Fig. 125. Closed ^ blastula, from shaken 8-celled stage ; 4 hours. 



Fig. 1 26. Four-celled stage from isolated macromere of 8-celled stage. 



Fig. 1 27. Eight-celled stage of the same individual. 



Fig. 128. Sixteen-celled stage of the same. Large cleavage-pore. 



Fig. 129. Thirty-two-celled stage of the same ; plate-form. 



Fig. 130. Later stage (another specimen); flat plate; 4 hrs. 



Fig. 131. Half -closed y^ blastula, with the last. 



Figs. 132, 133. Two curved plate-forms, y% embryos, 6 hrs., ^osely corres- 

 ponding with fragments of normal ectoblast and entoblast of the gastrulas at this 

 stage. 



Fig. 134. Curved plate-form, ^ embryo; 16 hours, free-swimming in life. 



Fig. 135. Closed y% blastula with last. 



