DEPARTMENT OF EMBRYOLOGY. 93 



Hitherto our information regarding sex ratio in man (the proportion 

 of males to every 100 females) has been derived from statistics of the 

 new-born and adult, while the sex ratio in uterine life has been repre- 

 sented only by a few conflicting estimates. The paper of Dr. A. H. 

 Schultz on this problem is, therefore, of especial interest. His study 

 is based upon 600 fetuses from the Carnegie Collection and 57 addi- 

 tional ones published by Rauber. 



Dr. Schultz distinguishes between the sex ratio at the time of 

 conception, which he terms original or primary sex ratio, and that at 

 birth and in the adult, which he terms respectively as secondary and 

 tertiary. After outlining the changes in sex ratio during the secondary 

 and tertiary periods, due to the unequal mortality of the two sexes, 

 he discusses the factors involved in the primary sex ratio, and partic- 

 ularly the relative frequency of abortions and stillbirths of the two 

 sexes. In general he finds that the sex ratio of intrauterine mortality 

 is higher than that of the living fetuses. As it is not possible to deter- 

 mine the sex by external examination in the first two months of preg- 

 nancy, there are no data for this period. In the third month the 

 mortality of males is about 25 per cent higher than that of females. 

 From the fourth to the seventh month it is nearly equal in the two 

 sexes. During the eighth to the tenth month the relation again shows 

 a higher mortality for the males. The author concludes that more 

 males, to the extent of not more than 10 per cent, are conceived, and 

 that at certain periods of pregnancy the relative mortality of males 

 exceeds that of females by as much as one-fourth. 



In a critical discussion of the changes in the sex ratio of new-borns 

 it is pointed out that most of the factors claimed to affect the ratio, 

 such as pelvic diameters of the mother, Jewish race, social class, 

 illegitimacy, war, etc., are not sex-determining but sex-eliminating; 

 i. e., they increase or decrease the relative frequency of abortions and 

 stillbirths with their high sex ratio, thus altering the primary sex 

 ratio during the period of pregnancy. 



The matter thus far referred to in this report deals with problems 

 of human embryology in its more general aspects. Other studies that 

 have been published during the past year will now be referred to under 

 two separate headings — cytology, and studies concerning individual 

 systems. 



CYTOLOGY 



The activities of this department in the field of cytology have 

 continued along lines similar to those of last year. They include a 

 group of studies based upon tissue cultures and another group based 

 upon fixed material and dealing particularly with the subject of 

 chondriosomes (mitochondria) . 



By means of tissue cultures M. R. Lewis and W. H. Lewis have 

 been able to make important observations on the growth and behavior 



