94 CARNEGIE INSTITUTION OF WASHINGTON. 



those of Metz on chromosomal homologies and chromosomal fragmentation, 

 elevate the chromosome to the position of the principal mechanism of heredity 

 and evolution. It illustrates the slowness with which new discoveries filter 

 into popular knowledge that the very name of the chromosome — so fateful 

 for mankind and civilization — should still be almost unknown outside of 

 genetic circles and sometimes insufficiently regarded and recognized even by 

 active biologists. To the geneticist, however, the chromosome with its genes 

 affords another precious link between the complex phenomena of the develop- 

 ment of the individual on the one hand and the constitution of matter on the 

 other. There is certainly much in the phenomena of gene mutation with its 

 prevailing recessive tendency, its measurable rate of occurrence, and its 

 predictability, that shows at least many points of similarity to the gradual 

 changes, by loss, of the salts of the uraniun-radium-lead series. 



In earlier reports much emphasis has been laid on the fundamental biological 

 phenomenon of sex, and regret has been expressed that we were able to enter 

 so inadequately into that field, for whose investigation we have special 

 facilities. Yet marked progress has been made during the current year in an 

 understanding of the nature of sex. For some years Dr. Riddle has demon- 

 strated that the pigeon's egg that is destined to produce a female has more 

 stored food material than an egg that is destined to produce a male. He 

 has been inclined to conclude that the special metabohc environment of the 

 early embryo was the cause of its becoming a female. Other biologists have 

 emphasized the role of the sex-chromosome in determining sex. But the two 

 views are not irreconcilable, inasmuch as the chromosomes are, doubtless, 

 regulators of the metabolism of the cell; but other conditions may control 

 cell metabolism and in so far sex. Dr. Riddle, however, has forged a new 

 link in the evidence of the influence of metabolism on sex. Pigeons forced 

 to lay excessively lay an excess of large, female eggs. Ovulation is associated 

 with a functional enlargement of the suprarenal glands; suprarenal hyper- 

 activity causes an increase of sugar in the blood. This provides more food 

 for the eggs at the time of maturation. This is probably why more large 

 (or female) eggs are laid during the period of enforced, excessive ovulation. 



In Cladocera, also, progress has been made in isolating the factor or factors 

 that bring about the production of males. The evidence indicates that the 

 determination of sex takes place at the time of maturation of the partheno- 

 genetic egg and that something in the water of overstocked culture-vials 

 influences the processes of maturation so that some of the eggs will develop 

 into male individuals. 



The opportunities for investigation in the field of genetics are limitless, and 

 the field touches vast human interests in agriculture, physiology, and applied 

 eugenics. In the past we have prospected rather widely, with the aim of 

 finding the best lodes to work. With our limitation in resources and with 

 fertile subjects of research in hand, it is clearly advantageous to concentrate 

 upon a few of the most productive of them. Thus we are gaining in unity, 

 and profit by the mutual criticism and cumulative ideas that come from 

 cooperation. 



