190 



SCIENCE. 



[N. S. Vol. XXIII. No. 579. 



ratio between the nuclear and the protoplasmic 

 mass (the ' Kernplasmarelation,' expressed by 

 the formula h/p) tends towards a normal value 

 that is in the long run constant for the species, 

 though it undergoes cyclical changes both in 

 the individual cell and in successive genera- 

 tions of cells. In ordinary or ' functional ' 

 growth the value of h/p undergoes a tem- 

 porary, decrease, owing to the more rapid 

 growth of the protoplasm, but this induces a 

 subsequent more rapid ' divisional ' growth of 

 the nucleus which raises the value of k/p to 

 a point above the normal, and finally leads to 

 cell-division by which the normal ratio is 

 again approximately restored. Long-contin- 

 ued ' autogenous ' (i. e., vegetative or asexual) 

 reproduction causes, however, a gradual per- 

 manent increase in the value of k/p (i. e., a 

 nuclear hypertrophy) and this necessitates a 

 reorganization by conjugation through which 

 the normal condition is restored. The value 

 of k/p may also be experimentally altered by 

 conditions of . food, temperature and the like; 

 and here, according to Hertwig's view, lies the 

 possibility of affecting the sexual relations by 

 external conditions. 



Professor Hertwig's application of this con- 

 ception to sex-production in the metazoa is, 

 we think, open to serious criticism. His cen- 

 tral assumption is that the ' Kernplasmarela- 

 tion ' differs in the two sexes, having a higher 

 value in the male {i. e., the nuclear mass is 

 assumed to be relatively greater in that sex), 

 and any influence that tends to increase this 

 value, whether in the gametes, in the zygote, 

 or in the developing embryo, favors or de- 

 termines the production of the male condition, 

 and vice versa. Since the egg contributes tc 

 the germ the entire mass of protoplasm and 

 half the nucleus, while the spermatozoon con- 

 tributes only half the nucleus, ' the egg nat- 

 urally takes the lion's share ' in the determina- 

 tion of the ' Kernplasmarelation ' and hence 

 in the determination of sex. In case of the 

 frog, over-ripe and under-ripe eggs tend alike 

 to produce males, because in the former (long 

 retained in the oviduct) the nuclear substance 

 has increased at the expense of the protoplasm, 

 while in the latter the protoplasm has not yet 

 completed its growth — either case giving a 



relatively high value to k/p. In view of the 

 fact that the nucleus breaks down and the first 

 polar spindle is formed at the time the egg 

 leaves the ovary, this explanation does not 

 seem very convincing, at least in the case of 

 over-ripe eggs. As applied to the cases of 

 Simocephalus and Dinophilus the argument 

 becomes too involved for detailed review here, 

 since the two cases are diametrically opposed, 

 a higher temperature favoring in the one a 

 continued production of parthenogenetic fe- 

 males, and in the other the production of 

 males ; but here too Hertwig attempts to show 

 that an explanation may be found in the as- 

 sumption of alterations in the value of Ic/p 

 directly or indirectly traceable to the effect of 

 temperature. 



It is somewhat surprising to find on how 

 small a basis of actual fact the central as- 

 sumption of the hypothesis rests. No new 

 cytological evidence is brought forward, and 

 the only facts given in direct support of the 

 assumption are, first, that the value of k/p is 

 enormously greater in the spermatozoon than 

 in the egg, and secondly, that in all cases 

 (such as Dinophilus) where male and female 

 eggs are distinguishable before fertilization 

 the former are smaller than the latter. It is 

 difficult to see how the first of these facts bears 

 on the problem, for the question is how the 

 male or female value of k/p is produced in 

 the zygote, which results from the fusion of 

 one gamete from each sex whether it pro- 

 duces a male or a female. The second fact is 

 assumed by Hertwig to mean that the male- 

 producing eggs have a relatively high value 

 of k/p, owing to a deficiency of protoplasm. 

 ' JSTach allem, was wir iiber Bef ruchtung wis- 

 sen, miissen die Kerne dieser Kleineier (of 

 Dinophilus) ebenso gross sein, wie die der 

 Grosseier ' (p. 196). But Korschelt's figures 

 of Dinophilus show the nuclei of the small 

 eggs very much smaller than those of the large 

 ones, ,in the ovaries, in the new-laid eggs 

 within the capsules, and in the early and late 

 cleavage-stag'es, and there is no actual evi- 

 dence, either in these eggs or in any of the 

 other cases, that the value of k/p is greater 

 in the males than in the females. On the con- 

 trary, in the only known cases of nuclear dif- 



