98 John H. Geroüld, 



to 3B and 3d, the latter being of about the same size as the other 

 blastomeres of the third quartet. 



The cells of the anterior hemisphere, althoug-h larger than those 

 of the second quartet, divide later, with equal cleavage, so that, 

 when the thirty-two-cell stage is reached, there are in each of the 

 quadrants A, B, and C, of the anterior hemisphere four relatively' 

 large cells of nearly equal size (Fig. 25). These are (1) an apical 

 cell, which is to furnish a blastomere of the rosette and one of the 

 cross, (2) an intermediate cell, which is to form the two intermediate 

 girdle cells, (3) two trochoblasts, which are to divide once more and 

 give rise to the cells of the primary prototroch. 



In the posterior hemisphere in each of the quadrants A, B, 

 and C, are four cells, viz. the two derivatives of the second quartet 

 (a minute anterior and a larger posterior cell), the third micromere, 

 and the basal, or posterior, blastomere. Only one of these four 

 equals in size the blastomeres of the anterior hemisphere, viz. the 

 last-mentioned. 



The dorsal quadrant in the anterior hemisphere is like the three 

 others but, in the posterior half of this quadrant, 2d, an enormously 

 large cell, divides unequally (Fig. 37), and the anterior product of 

 this division becomes covered by the trochoblast that lies immediatlj^ 

 in front of it (Fig. 38). 21) divides to form 3d and 3D. 



i 



Fig. C. 



Apical cells iu Ph. vulgare. A slightly later stage of the same egg shown in 



Fig. 35. Rosette (la'-i-'—irZ'-i-ij. Cross cells {la^-^-'^—W-^-'^) iu oue which, Ic'-^-"^, 



a spindle is seen. Intermediate mother cells {la^-" — Id^--). In Ih'^-'- a radial, 



slightly laeotropic spindle is present. -Zc'-^ has already divided. 540 : 1. 



