Ciur. VIII. Proportion of the Sexes, 255 



less information. With Spiders, Mr. Black wall, who has carefully 

 attended to this class during many years, writes to me that the males 

 from their more erratic habits are more commonly seen, and therefore 

 appear inure numerous. This is actually the ease with a few species ; 

 but he mentions several species in six genera, in which the females 

 appear to be much more numerous than the males. 91 The small size of 

 the males in comparison with the females (a peculiarity which is some- 

 times curried to an extreme degree), and their widely different appear- 

 ance, may account in some instances for their rarity in collections. 92 



Some of the lower Crustaceans are able to propagate their kind 

 nsexually, and this will account for the extreme rarity of the males: 

 thus Von Siebold 93 carefully examined no less than 13,000 specimens of 

 Apus from twenty-one localities, and amongst these he found only 

 310 males. With some other forms (as Tanais and Cypris), as Fritz 

 Miiller informs me, there is reason to believe that the males are much 

 shorter-lived than the females ; and this would explain their scarcity, 

 supposing the two sexes to be at first equal in number. On the other 

 hand, Miiller has invariably taken far more males than females of the 

 Diastylidse and of Cypridina on the shores of Brazil; thus with a 

 species in the latter genus, 63 specimens caught the same day included 

 57 males ; but he suggests that this preponderance may be due to 

 some unknown difference in the habits of the two sexes. With one 

 of the higher Brazilian crabs, n.miely a Gelasimus, Fritz Miiller 

 found the males t:> be more numerous than the females. According 

 to the large experience of Mr. C. Spence Bate, the reverse seems to 

 be the case with six common British crabs, the names of which he 

 has given me. 



The proportion of the sexes in relation to natural selection. 

 There is reason to suspect that in some cases man has by 

 selection indirectly influenced his own sex-producing powers. 

 Certain women tend to produce during their whole lives more 

 children of one sex than of the other : and the same holds good 

 of many animals, for instance, cows and horses ; thus Mr. Wright 

 of Yeldersley House informs me that one of his Arab mares, 

 though put seven times to different horses, produced seven 

 fillies. Though I have very little evidence on this head, analogy 

 would lead to the belief, that the tendency to produce either 

 sex would be inherited like almost every other peculiarity, for 

 instance, that of producing twins ; and concerning the above 

 tendency a good authority, Mr. J. Downing, has communicated 

 to me facts which seem to prove that this does occur in certain 

 families of short-horn cattle. Col. Marshall 91 has recently found 

 on careful examination that the Todas, a hill-tribe of India, 



n Another great authority with 0. P. Cambridge, as quoted in 



"espect to this class, Prof. Thorell of 'Quarterly Journal of Science,' 



Opsaia (' On European Spiders,' 1868, p. 429. 



1869-70, part i. p. 205) speaks as if 93 ' Beitriige zur Parthenogenesis,' 



female spiders were generally com- p. 174. 



moner than the males. ?i 'The Todas,' 1873, pp. 100 



•* See, on this subject, Mr. Ill, 194, 193. 



