268 Preponderance of Males and Females in Fish 



constitution XX. In support of this conclusion based on genetical 

 evidence, is the work of Strasburger ('00 and 10) and Doncaster ('12), 

 who found that female plants of L. dioica when attacked by the anther- 

 smut (Ustilago violacea) were transformed towards hermaphroditism 

 (which is thus purely somatic in the sense adopted by Shull). 



Morgan ('19, p. 188) believes that Hertwig's and Kuschakewitsch's 

 results may be due to " late-fertilized " eggs being in reality not fertilized 

 at all, but partheno- or arrheno-genetic. There is as yet, however, no 

 direct evidence in favour of this view, while the case of Lychnis shows 

 that sex-chromosome constitution may be overridden, at least so far as 

 to give hermaphroditism. 



Steinach ('12 and '13) has conclusively shown that the secondary 

 sexual characters of male (presumably XY) rats can be overridden by 

 the extirpation of the testis and implantation of an ovary; and Lillie (17') 

 has shown that in female (presumably XX) embryos of cattle twinned 

 with males, the development of the gonad itself is altered, and it and 

 all the internal accessory sexual organs are caused to become more male 

 than female, by means of the circulation in the blood of substances 

 emanating from the male twin ; i.e. the primary sex-characters can be 

 modified in the zygote, and therefore apart from chromosomes. In 

 Crustacea, Smith ('06) has given the reverse proof; the males of 

 Inachus, upon recovery from parasitic castration, are switched over 

 towards femaleness, ova being actually formed in their gonads. 



There remains a further set of cases which are possibly capable of 

 another interpretation. Goldschmidt ('16) and Harrison ('19) with moths 

 and Riddle ('16) with pigeons have shown that inter-generic, -specific 

 or -varietal crosses give a large excess, often up to 100°/^, of males (in 

 these groups, the homogametic sex). In addition. Riddle has shown that 

 a large excess of females maybe produced by various depressing agents. 

 The results are certainly not due to differential mortality. In the 

 pigeons Strong ('12) has, however, proved that all the animals must 

 have the chromosome-constitution normal to their sex. This he accom- 

 plished by breeding experiments involving a sex-linked character. 

 This is further established by the data given by Riddle himself. The 

 only hypothesis for the pigeons would therefore seem to be that the 

 stimulating effect of foreign sperm causes the TT-chromosome to be 

 thrown out in the polar body, while depressing agents cause it to 

 remain in the egg (it should be noted that at fertilization the first 

 maturation spindle is in its metaphase). This cannot be the operating 

 cause in the frog, if that animal is of the XX, XY type, for both egg 



