256 LILLIE. [Vol. XVII. 



The behavior of the spheres in the first cleavage is entirely 

 similar to that of the egg-sphere during the copulation phases 

 of the germ-nuclei. The enlargement of the inner spheres 

 begins during the anaphase (PI. XXVII, Fig. 47) and goes on 

 rapidly during the telophase, until a large amount of sphere 

 substance is produced (PL XXVII, Figs. 48 and 49). The 

 sphere substance then elongates in the direction which the 

 second cleavage spindles will assume much later (PI. XXVII, 

 Fig. 50, horizontal section, and Figs. 51 and 52, vertical section, 

 of the larger cell CD). At the same time each cell takes 011 the 

 form of a dividing cell (seen especially well in the larger cell, 

 PI, XXVII, Figs. 50-52), although the mtclei are not yet recon- 

 structed since the preceding division. I regard this as a prema- 

 ture expression of the forces within these cells that later cause 

 an unequal division in the region of the constrictions, after the 

 spindles have been formed. Later both cells round off, then 

 become closely appressed, and, when the spindles form, they 

 move into the positions previously indicated by the elongation 

 and constriction of the cells and sphere substance. 



The sphere substance is thus divided in both the first and 

 second cleavages ; from its position and form it seems likely 

 that it is distributed between the cells very nearly in propor- 

 tion to their size. It is, however, impossible to be certain of 

 this, because one cannot follow it in any division up to the 

 time of the definitive placing of the spindle ; before this time 

 the intrusion of yolk-granules on it has hidden it from view. 



V. Concerning the Sphere Substance. 



From the preceding account it will be plain that I regard the 

 entire sphere substance as the product of growth or inflation 

 of a single centrosome. There can be no doubt that it is de- 

 rived from the inner sphere, so that everything depends on the 

 interpretation of this structure. On pp. 240-242 I have given 

 in detail my reasons for believing that each of the inner spheres 

 of the second maturation spindle is derived from a single cen- 

 trosome. I can add nothing to the description there given, 

 except the statement that I have worked over this series of 



