22 



SCIENCE 



[N. S. Vol. XL VI. No. 1175 



determined by Benedict and Emmes;^ they find 

 that the metabolism of man is 5 per cent, to 6 

 per cent, higher than that of woman. 



Have we any measure of either of our dif- 

 ferentials in any mammalian egg? I think 

 that the experiments on sex-determination in 

 cattle, together with an observation by van der 

 Stricht, aiford some evidence that the water- 

 content of the male-producing egg is high, and 

 that of the female-producing egg is low. 

 Thury reported in 1862 that from fertilizations 

 made in the early period of heat in cattle an 

 excess of females were produced; and that 

 later (delayed) fertilizations give rise to an 

 excess of males. Similar experiments have 

 been four or five times repeated by others, and 

 these have all shown an excess of one or the 

 other sex in accordance with such early or late 

 fertilization." ISTo one definitely knows whether 

 the ovTim of the cow absorbs water in the Fal- 

 lopian tubes in this interval between ovulation 

 and fertilization, but we do know that every 

 amphibian, reptilian and avian egg that has 

 been investigated does absorb very appreciable 

 amounts of water while being passed from the 

 ovary to the exterior. And, van der Stricht 

 has described phenomena of growth or swell- 

 ing of the yoke granules in one mammal — the 

 bat — which, I am sure from my own studies on 

 yolk, indicate the taking up of water by the 

 egg of this mammal. It is highly probable, 

 therefore, that precisely that time relation 

 which leads to an excess of males in cattle is 

 preceded or accompanied by an increased hy- 

 dration of the ovum. In mammals therefore 

 there is some evidence that a shift of the meta- 

 bolic level — as indicated by one partly known 

 sex-differential — is associated with the ob- 

 served changes in the sex-ratio of the germs 

 which are thus modified. Further, in one 

 adult mammal — man — two of the three sex- 

 differentials have been definitely demonstrated. 

 These results for both the egg and adult 

 stages of the mammal are at every point in 



8 Jour. Biol. Cliem., Vol. XX., 1915. These au- 

 thors give references to earlier literature. 



8 The use of the terms early and late fertiliza- 

 tions assumes that some ovulation occurs either im- 

 mediately before, or shortly after, the beginning 

 of heat. 



complete agreement with our data for both the 

 egg and adult stages of the bird. 



Experiments on the frog and the toad have 

 afforded evidence for the control of sex. This 

 evidence by many is not thought conclusive. 

 Though selective fertilization has been elimi- 

 nated as a possibility by Kuschekewitch there 

 remains the possibility of parthenogenetic de- 

 velopment to account for the excessive male- 

 production in his experiments with the frog. 

 But this appeal makes it impossible to explain 

 the great excess of females obtained by Dr. 

 King on the eggs of the toad, and leaves such 

 doubters to lean here upon the discredited staff 

 of selective fertilization — a proposition wholly 

 disproved for the related frog and for the 

 pigeon. 



How does this situation look in the light of 

 the sex-diilerentials already noted for birds 

 and mammals? Richard Hertwig,^" and later 

 Kuschekewitch,!! allowed frog-'s eggs to over- 

 ripen — a process during which the eggs tahe up 

 water — and obtained (in the case of the latter 

 author) in some cases a total of 100 per cent, of 

 males. Dr. King^^ did the converse of this ex- 

 periment with toad's eggs — withdrawing water 

 from them before fertilization — and obtained 

 nearly or quite 90 per cent, of females in cases 

 where the mortality was less than 7 per cent. 

 According to our knowledge of the sex-differ- 

 entials in the pigeon's eggs both of these ex- 

 periments might have been predicted to result 

 as these three investigators have reported. 



In the spider-crabs Geoffrey Smith^^ has 

 shovsm. that both the blood and the liver of the 

 adult male crabs contain less fat than do the 

 blood and liver of the females. Here once more 

 the facts concerning one of the sex-differentials 

 is in complete accord with all the preceding 

 cases. In the parasitically castrated spider- 

 crabs Smith and Robson were able to show, 

 moreover, that the parasitized male crahs, 

 which under these conditions gradually as- 

 sume several female morphological character- 

 ed Verhand. deutsch. zool. Gesellsch., 1906. 



11 Festschrift, f. B. Hertwig, 1910. 



12 Jour, of Exp. Zool, Vol. 12, April, 1912. 



13 The Quart. Jour, of Micr. Sci., Vol. 57, No- 

 vember, 1911. 



