708 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Factors of Sexuality.*— K. Diising commences by discussing the 

 correlation of the organs, and reminds us of the familiar fact that 

 agriculturists are in the habit of removing the genital organ from 

 those individual cattle that they wish to fatten. It is next pointed out 

 that in nearly all cases where organs disappear, as for example in 

 parasites, the reproductive apparatus is always retained, while, on the 

 other hand, in sterile hybrids there is a marked development of the 

 organs which preserve the life of the individuals. 



With regard to the proportional relations of the sexes, we have some 

 statistical observations ; to these the author now adds some consider- 

 ations from the point of view of the doctrine of natural selection, and 

 he points out that the numerical supremacy of one sex may be of 

 considerable advantage in the development of a large progeny. He 

 thinks, further, that it is possible to demonstrate mathematically that, 

 where there is an abnormal relation of the sexes, an animal which 

 produces a large number of the kind of individuals that are wanting 

 will leave more descendants than one that does not do so. This 

 peculiarity will, in time, be confirmed by natural selection. In 

 illustration of this reference may be made to what seems to be a 

 statistical truth ; late fertilization of women tends to the production 

 of males, and, in all circumstances, the first-born are, in the majority 

 of cases, boys. Further, the author believes that statistics show 

 that after a war there is a large preponderance of male babes. 



"Where, among cattle, demands are largely made on an individual 

 bull, the majority of his progeny are males, and this is because young 

 spermatozoa tend to produce males ; this view of the different value 

 of spermatozoa of different ages has the support of so high an authority 

 as Prof. Preyer. Eeduced to a general law, the results may be thus 

 enunciated : the larger the want of individuals of one sex, the more 

 frequently are their genital products required, and, therefore, the 

 more frequently do the minority produce young of their own sex. 

 The investigations of Thury have shown that young ova tend to form 

 progeny of the female sex, while delayed fertilization leads to the 

 production of males ; the calves of the earlier stages of the rut are 

 more frequently females than those of the later. 



The indirect causes which are equivalent to an absence of indi- 

 viduals are (a) insufiicient nutrition ; the effect of this is seen in the 

 the fact that a well-fed cow served by a starved bull always produces 

 males, and inversely. In other words, there is a close connection 

 between nutrition and reproductive capacity. (/3) Difference in age. 

 Every individual at the time of its highest reproductive capacity tends 

 to produce its own sex ; and the preponderance of males is greatest 

 when the male is considerably older than the female. This law was 

 discovered by Hofacker and Sadler, and is supported by the 58,000 

 cases reported on by Goehlert and Legoyt. 



We come, then, to this conclusion : Animals have by adaptation 



acquired the power, in the presence of abnormal sexual relations, of 



producing more individuals of the sex of which there is a want ; and 



the same balance is maintained by the same methods when there are 



* Jenaisch. Zeitscbr. f. Naturwiss., xvi. (1883) pp. 428-64. 



