148 



Edwin G. Conklin. 



Normal Development of Cynthl\ partita, 4-Cell to 64-CELL Stages; X 333. 



The yellow crescent which surrounds the posterior half of the egg dorsal to the equator is stippled. 

 The gray crescent around the anterior border of the egg is left unshaded. The boundary between the 

 clear protoplasm and the yolk is indicated by a crenated line. The polar bodies (shaded by vertical 

 lines) lie at the animal or ectodermal pole. 



Fig. I . Four-cell stage from the animal pole, the yellow crescent showing through the egg. 



Fig. 2. Telophase of the third cleavage (8-cell stage), from the left side. 



Fig. 3. Twenty-cell stage from the animal (ventral) pole. 



Fig. 4. Twenty cells, transitional to the 24-cell stage, from the vegetal (dorsal) pole. The gray 

 crescent is now segregated in the two pairs of cells A^--, A^-^; the yellow crescent will be localized in 

 separate cells at the close of the division which has already begun in the cells B^-^. 



Figs. 5 and 6. Ventral and dorsal views of the same egg in the 64-cell stage. The yellow and 

 the gray crescents each consist of a double arc of cells; the anterior arc of the gray crescent (A^-*, A'-^) 

 is composed of neural plate cells, the posterior arc (A''-^, A^-''), of chorda cells; only two pairs of cells 

 in the yellow crescent (B''-*, B^-*) are muscle cells, the others are mesenchyme. The pair of. cells A^-* 

 also gives rise to mesenchyme. All the other cells of the dorsal hemisphere (Fig. 6) are endodermal. 

 All the cells shown in Fig 5, except those of the yellow and gray crescents, are ectodermal. 



