The President's Address. By J. Arthur Thomson. 145 



female even in young stages. But the most important criticism is 

 the first, which leads Beard, for instance, to say that Yung's experi- 

 ments are only of importance in regard to the relative viability of 

 the two sexes. 



It is necessary to have renewed experiments on a large scale, 

 and to have more precise data as to the time when the sex of the 

 tadpole is unmistakably distinguishable. One of the objections 

 raised against Yung's conclusions is that even in natural conditions 

 the percentage of females is sometimes very high, but we would 

 note that finding, say, 86 ' 8 p.c. of females in a collection of frogs 

 from a pond does not in itself prove that Yung's results were falla- 

 cious. There may have been, for instance, peculiar nutritive con- 

 ditions in the locality where the collection was made. 



7. Various observers — Landois, Treat, and Gentry — have noted 

 that when insufficient food is given to a crowd of caterpillars there 

 is an unusually large number of males. But as the sex of the cater- 

 pillar is said to be fixed when it leaves the egg, the experiments 

 were probably irrelevant, and the most that they showed was that 

 there are sometimes great differences in the rate of juvenile mor- 

 tality of the two sexes. Professor Poulton observes in regard to 

 the poplar hawk-moth (Smeririthus pojndi), for instance, that the 

 female larvae being larger require more food, and will therefore 

 starve first when supplies are scarce. Kellogg and Bell found that 

 the sex of the silkworm is not appreciably affected by the nutrition 

 of parents or even grandparents, and Cuenot found that the sex of 

 blow-fly larvae was not affected by what they ate or by what their 

 parents ate. 



8. It must be admitted, then, that there is no cogent evidence 

 to show that environmental influences operating on a developing 

 organism may decide what its sex is to be. On the other hand, 

 when we recall how a little nutritive attention makes a worker- 

 grub a queen-bee, or how Aphides produce females parthenogenetic- 

 ally through months (or even years) of high feeding and pleasant 

 temperature, and how the advent of autumn, with its cold and its 

 scarcity of food, is followed by a birth of males, and so on, we may 

 not be able to share the dogmatism of some who assert that the 

 theory of the environmental determination of sex is preposterous. 

 We shall consider in a subsequent section the question of the 

 influence of the environment on the parents. 



B. — Is the Sex quite Uxpredestined in the germ-cells 



BEFORE FERTILIZATION, AND IS IT THEN SETTLED BY THE 

 RELATIVE CONDITION OF THE GAMETES, OR BY A BALANCING 

 OF THE TENDENCIES THEY BEAR, NEITHER GAMETE BEING 

 NECESSARILY DECISIVE ? 



9. Hofacker (1823) and Sadler (1830) independently published 

 statistics in support of the theory that when the male parent is the 



