Plate IX. 



Surfact Views oj Entire Eggs of Cynthia partita; Forty-four to Tiro Hundred and Eighteen Cells, 



Figs. 128, 129. Same egg as shown in figs. 124-127. Fig. 128 from the left side; the equator of the 

 egg (plane of the third cleavage) is the heavy line running between A ami 1' and 

 separating cells designated by lower case from those designated by capital letters. Fig. 

 129. View from the posterior pole. 



Figs. 130 and 131. Ventral and dorsal views respectively of one and the same egg; 64 cells, 32 in 

 each hemisphere, distributed as follows: Ventral hemisphere, 26 ectoderm, 6 neural plate 

 cells (a 7 -', a 7 -', a 7- ' 3 ) ; Dorsal hemisphere, 10 endoderra, 4 chorda (A 73 , A 77 ), 4 neural plate 

 (A'-, A 7 - 8 ), 10 mesenchyme (B 7 - 6 , B 7 5 , B", B 73 , A 7 ' 6 ) and 4 muscle (B 78 , B 7 ->). 



Fig. 132. Postero-dorsal view of an egg in the same stage as the preceding showing direction of 

 division of mesenchyme cell (B 73 ). 



Figs. 133 and 134. Ventral and dorsal views respectively of one and the same egg; 110 cells; Ven- 

 tral hemisphere 64 cells, 52 ectoderm, 12 neural plate (a 8 ' 9 , a 8= , a 8 ' 7 , a 8 ' 8 , a 8,25 , a 8=6 ) ; 

 Dorsal hemisphere 46 cells, 10 endoderm, 8 chorda (A 85 , A 86 , A 8 - 13 , A 8 ' 4 ), 8 neural plate 

 (A 8 - 7 , A 8 - 8 , A 8 -' 3 , A 8 ' 6 ), 12 mesenchyme (B 7 - 6 , B", B 7 7 , B 8 ', B 86 , A 7 - 6 ), 8 muscle (B 8 - 7 , B 88 , 

 B 8 ' 5 , B 8 " 6 ). Gastrulation has begun. 



Fig. 135. Dorsal view of a slightly more advanced stage showing increasing gastrulation ; 118 cells, 

 ventral hemisphere 64 cells, dorsal hemisphere 54, viz., 10 endoderm, 16 mesenchyme, 12 

 muscle, 8 chorda, 8 neural plate; when the divisions indicated by spindles are completed 

 there will 4 additional endoderm and 2 additional mesenchyme cells. 



Figs. 136-139. Four views of one and the same egg; fig. 136 dorsal, 137 posterior, 138 anterior, 139 

 ventral; gastrulation well advanced. 124 cells; Ventral hemisphere 64 cells, 52 ecto- 

 derm, 12 neural plate (a 8 -'", a 8 -*", a 8 " 7 , a 8 ' 8 , a 8 - 23 , a 6 - 56 ); Dorsal hemisphere 60 cells, 14 

 endoderm, 8 chorda, 8 neural plate, 18 mesenchyme, 12 muscle. Spindles are already 

 present for divisions, which, when completed, will lead to 178 cells, viz., 96 ectoderm, 12 

 neural plate of ventral hemisphere, 12 neural plate of dorsal hemisphere, 8 chorda. 211 

 mesenchyme, 12 muscle, 18 endoderm. 



Figs. 140-143. Four views of one and the same egg; 140 dorsal, 141 posterior, 142 anterior, 143 

 ventral. Gastrulation is here far advanced. 180 cells; Ventral hemisphere 108 cells, 

 96 ectoderm, 12 neural plate; Dorsal hemisphere 72 cells, 12 neural plate of dorsal hemi- 

 sphere, 8 chorda, 20 mesenchyme. 12 muscle, 20 endoderm; when the divisions indicated 

 by spindles are completed there will be 4 additional neural plate cells. 



Figs. 144 and 145. Two views of the same egg; 144 dorsal, 145 median optical section in sagittal 

 plane. In fig. 145 the polar body is not visible, but its supposed position is indicated by 

 the dotted outline at the animal pole; the dotted outlines at the lower pole indicate the 

 mesoderm cells which lie in the lateral lip of the blastopore and out of the plane of the 

 section ; the rolling in of the muscle cells in the lateral lips is well shown. 



Fig. 146. Anterior view of an egg of about the same stage as the preceding, showing the division of 

 the 12 neural plate cells of the ventral hemisphere. 



Fig. 147. Ventral view of a similar stage with the ectoderm omitted in order to show the endoderm 

 and mesoderm from the ventral side. At this stag.' all the ectoderm cells have passed 

 into the 9th generation, all the endoderm into the 8th or 9th, all the mesoderm except 

 IV" into the 8th or 9th, all the chorda and neural plate cells into the 9th. There 

 are 218 cells; Ventral hemisphere 128 cells, 104 ectoderm, 24 neural plate of ventral 

 hemisphere; Dorsal hemisphere 90 cells, viz., 16 mural plate, 16 chorda, 20 mesenchyme, 

 12 muscle, 26 endoderm. 



