12 



BIOLOGICAL LECTURES. 



peculiar relations established by it. The cause of the inequa- 

 lity must lie in the undivided ovum, and a study of the first 

 cleavage-spindle shows that the inequality is unmistakably 

 foreshadowed before the least outward sign of division appears ; 

 for the asters at the spindle-poles are conspicuously unequal 

 in size, the larger aster corresponding with the future larger 

 cell (Diagram II). This difference is not connected with any 



determinable mechanical 

 conditions ; for the centro- 

 somes lie nearly equidistant 

 from the membrane (the 

 egg is spherical), and the 

 deutoplasm shows no per- 

 ceptible inequality in hori- 

 zontal distribution. The 

 conclusion seems unavoid- 

 able that the differentiation 

 in size is caused by a specific 

 form of activity in the 

 cytoplasm (or archoplasm), 

 occurring prior to cell-division. But if a differentiation in 

 size may have such an origin, we may fairly argue that other 

 differentiations may likewise precede cell-division, and that 

 in such cases the division may be, in a sense, qualitative. 



It seems to me, that in these considerations we may find, in 

 some measure, a reconciliation between the extremes of both 

 the rival theories under discussion — that we may consistently 

 hold with Driesch that the prospective value of a cell may be 

 a function of its location, and at the same time hold with Roux 

 that the cell has, in some measure, an independent power of 

 self-determination due to its inherent specific structure. Such 

 a view is only possible, however, if we regard the specific struc- 

 ture of the cell to have arisen not through the segregation and 

 isolation within its boundaries of special idioblasts or germ- 

 substances, that have been sifted out by qualitative division, 

 but through a physiological specialization (as de Vries oxA 

 Hertwig insist) that may have taken place before, during, or 

 after cell-division, according to circumstances. If differentia- 



DlAGKAM II. 



