514 KNOWER. [Vol. XVI. 



material. There can be little doubt, however, that a typical 

 series is here figured, for the figures are based on an examina- 

 tion of a great many specimens, and the chief stages are well 

 marked. 



Since the first rudiment of the embryo is formed from 

 surface cells alone, the few yolk-cells may be neglected in 

 the description. 



PI. XXIX, Figs. 7-10^ represent successive changes on the 

 surface of older eggs. The nuclei are found at all points on 

 the surface in the act of dividing, or in pairs just subsequent to 

 division. In the posterior half of the Q.gg this activity becomes 

 especially pronounced, while the nuclei of the anterior half are 

 comparatively inert. 



Three surfaces of a somewhat older Q,g^ are shown in PI. 

 XXIX and PI. XXX, Figs, ii-iit- (ventral, dorsal, and lateral 

 views). As compared with the preceding figures and with the 

 following ones, it is evident that the number of cells in the 

 anterior half of this egg has reached a maximum, which remains 

 constantly about the same in older specimens. The nuclei in 

 this half are few and widely separated. The opposite end, on 

 the other hand, is the seat of active multiplication and change. 

 This is true of the whole posterior end, but it is evident in the 

 three views of the egg before us that the dorsal (PI. XXX, 

 Fig. 11^) and lateral (PI. XXX, Fig. ii^) surfaces of this half 

 are less crowded with nuclei than is the ventral side. The 

 ventral surface (PI. XXIX, Fig. 1 1) exhibits an extensive area of 

 rather closely crowded nuclei, stretching to the extreme limits 

 of the surface posteriorly and laterally. A side view (PI. XXX, 

 Fig. 11^) shows a considerable lateral extension of this area, 

 relatively crowded as compared with the rest of the surface. 



The posterior half of the surface represented in PI. XXIX, 

 Fig. 10, exhibits an activity in division and a distribution of 

 nuclei of about the same intensity in its entire extent, forward 

 to the shorter diameter of the egg. A line drawn through the 

 shorter diameter of this figure divides rather sharply an ante- 

 rior half, with but few widely separated nuclei, from a posterior 

 half, in which the nuclei are more numerous and lie compara- 

 tively close together down to the line just drawn. Near the 



