EwART — Variation: Germinal and Environmental. 367 



irrespective of the general condition, may be better nourished in one individual 

 than another. 



Again, the ova discharged at the outset of the reproductive period may in 

 various respects, differ from ova formed later, and these may again differ from 

 ova produced as senescence supervenes. 



Coming now to the second stage, the extremely important and much-discussed 

 question arises — " Does the protoplasm discharged from the nucleus in the second 

 polar body differ from the protoplasm retained, i.e. is the reduction qualitative as 

 well as quantitative ? " If during reduction it is possible for the germ-plasm 

 representing the immediate or intermediate ancestors of any individual or group 

 of individuals to escape, we may have in the " reducing division " a sufficient 

 means of accounting for a certain amount of variation.* 



During the third stage, i.e. during the time that intervenes between the 

 " reducing division " and the union with the spermatozoon, the changes which 

 take place may have no small influence in settling the fate of the new individual. 

 That important changes occur in ova not only before and during maturation, but 

 especially after the escape of the polar bodies, may be assumed by the difference 

 in the staining-reaction of the nucleus. In the newt, e.g.., according to Watas(^,t 

 germ-nuclei not only stain differently throughout the whole period of their 

 maturation, but also up to the end of fertilization. It almost appears as if conju- 

 gation were impossible in some cases until certain chemical or johysical chano-es 

 occur in the matured ovum, or in its immediate environment. The Hertwigs % 

 e.g. showed that when the vitality of ova was diminished by shaking them in 

 water and allowing them to stand for some time, cross-fertilization was more easily 

 accomplished, while Born§ found that cross-fertilization was expedited by adding 

 a superbundance of sperm. It has also been proved by Vernon that the stale germ- 

 cells of echinoderms behave after a time very differently from fresh germ-cells. 

 Up to a certain time the development is normal, then there is about 1 per cent, of 

 abnormal blastulse per hour, after which the number of abnormal blastuloe may be 

 nearly 20 per cent, per hour. What is, perhaps, more remarkable is, that stale 

 sperms give, with fresh ova, larvse distinctly larger than when both sperms and 

 ova are fresh, while stale ova with fresh sperms produce abnormally small larvie. 



* Weismann's theory of heredity takes for granted that the germ-plasm discharged in the polar bodies 

 may be quite different from the germ-plasm whieh remains to conjugate with the entering spermatozoon. 

 It may never be possible by direct observation to prove whether this assumption is or is not warranted ; 

 but it may be possible by experiment to prove, on the one hand, that it is an inadequate explanation, and, 

 on the other, that cumulative diiferences ia the nutrition, ripeness, &c., of the germ-ceUs are sufficient to 

 account for much of the variation we find in organic nature. 



t Wilson, "The Cell," p. 127. | Jenaische Zeitsclirift f. Medicin, vol. 19 (1886). 



§ Pfliiger's Archiv, vol. 32, p. 453. 



