194 Edwin G. Conklin 



Anterior and Posterior Half Gastrulae. 



Figs. 77-82. Partial embryos derived from gastrulae of the stage shown in Fig. 8, which were cut 

 in two transversely so as to leave the whole of the yellow crescent in one half. The chorion is shown 

 as a line around the embryos. Figs. 77, 78. Dorsal and ventral views respectively of one and the 

 same embryo, drawn 19 hours after the operation. A mass of cellular debris lies between the two half 

 embryos; the endoderm cells are chiefly contained in the anterior half, the mesenchyme and muscle 

 cells are entirely confined to the posterior half. Neither half at all resembles a normal embryo or larva. 

 Figs. 79, 80. Ventral and postero-dorsal views of another embryo, 19^ hours after the operation. 

 The crescent of yellow cells is entirely confined to the posterior half and neither half resembles a normal 

 larva. Fig. 81. Anterior and posterior half embryos 20 hours after the operation. Fig. 82. Pos- 

 terior half embryo from the postero-dorsal side, 20 hours after the operation. The anterior half is 

 degenerating and is shown only in dotted outline; the posterior half contains all of the yellow cells and 

 practically no endoderm. At the stages represented by all these figures the normal embryos have 

 already undergone their metamorphoses. 



