286 



CELL-DIVISION AND DEVELOPMENT 



may be entirely re-arranged under the influence of gravity, and a 

 new axis established. In sea-urchins, my own observations ('95) 

 render it probable that the egg-axis is not finally established until 

 after fertilization. Finally, it is becoming more and more doubt- 

 ful whether the relation of the egg-axis to the adult axis has so deep 

 a significance as was at first assumed. This relation has been found 



Fig. 130. — Variations in the axial relations of the eggs of Cyclops. From sections of tlie eggs 

 as tliey lie in the oviduct. [Hacker.] 



A. Group of eggs showing variations in relative position gf the polar spindles and the sperm- 

 nucleus (the latter black) ; in a the sperm-nucleus is opposite to the polar spindle, in b, near it or 

 at the side. B. Group showing variations in the axis of first cleavage with reference to the polar 

 bodies (the latter black) ; a, b, and c, show three different positions. 



to vary not only in nearly related forms (insects), but even in the 

 same species {Ascaris, according to Boveri and others ; Toxopncnstcs, 

 according to my own observations; copepods, according to Hacker). 

 All these and many other similar facts force us, I think, to the 

 conclusion that the promorphological features of the Q.^g are as truly 

 a result of development as the characters coming into view at later 



