ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 215 



such as North America and Australia, there is a preponderance of 

 male births. 



These principles may be applied to thelytoky which is caused and 

 conditioned by an over supply of females, to arrenotoky, where one 

 female is fertilized, and to asexual generation whether by fission, gem- 

 mation, or pedogenesis. The same rules will apply to plants. 



It is a great advantage to be hermaphrodite as long as possible, as 

 the tendency towards one sex can be altered at a comparatively late 

 period in embryonic life; as we know, the embryos of nearly all 

 animals are at first hermaphrodite. 



Causes of Sex.* — J. Schlechter has investigated the reproduction 

 of horses ; dealing with 2064 births, and examining first of all the 

 influence of the absolute and relative ages of father and mother, he 

 finds that the proportion of female to male births was as 100 to 91 • 3 ; 

 where the sire and dam were of the same age and between four and 

 twelve years of age more females were born, but when they were 

 between twelve and sixteen a considerably larger number of males. 

 When the sire was older than the dam a larger number of males were 

 born where the difference was slight, and a larger number of females 

 when the difference was more extensive. When the dam was the 

 older a larger number of fillies was produced. 



The second problem is that of the influence of the first and of later 

 copulations. on the resulting sex; fillies were to young horses as 100 

 to 90*2 where the dams were covered for ,the first time; and the 

 proportion was exactly the same where the dams had already been 

 mothers. The time of year has this importance, that females are 

 produced to males in the proportion of 100 to 90*2 in the cold months 

 of the year, and as 100 to 89-5 in the warmer months. More males 

 seem to be produced when the virile activity is at its highest point ; 

 males are on the average eight-tenths of a day longer during the 

 gestation period. The first-born are rather more frequently males. 



H. Bernerj demonstrates that the hypothesis of Hofacker and 

 Sadler, which explains the excess of boys born in Europe to' the fact 

 that the husband is ordinarily older than the wife is untenable. The 

 author's results are based on the Norwegian statistics of population 

 for 1871-5 ; there were 213,224 births, 109,431 of which were boys, 

 or a proportion of 105-43 boys to 100 girls. Where the parents were 

 of the same age, the proportion of boys to girls was as 106 • 23 to 100 ; 

 when the father was one to ten years older, as 104 • 61 to 100 ; where he 

 was more than ten years older, as 103-54 to 100 ; where the mother 

 was one to ten years older than the father, as 107-45 to 100; where 

 she was more than ten years older, as 104-10 to 100. On the whole, 

 then, the results are just contrary to what we should expect from 

 Hofacker and Sadler's hypothesis. Berner approves of the doctrine 

 of Richarz that, if the mother is specially fertile, a boy, that is, the 

 higher and more complete developmental form of the genus Homo is 



* Eev. f. Thierheilkunde, 1884, Nos. 7 and 8. Cf. Biol. Centralbl., iv. (1884) 

 pp. 627-9. ' V ^ 



t 8vo, Cbristiania, 1883, 70 pp. Biol. Centralbl., iv..(lS84) pp. 461-5. 



