Chap. VIII. Proportion of the Sexes. 255 



loiis information. Witi Spirlera, Mr. Blaokwall, who has carefully 

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

 from their moi'e erratic; habits aie more ooinmoiily seen, and therefore' 

 sppe ir mcire numerous. This ia actually the case with a few species ; 

 but he njentious several species in six genera, in wliich tLo females 

 »p|iear to lie much moie numinius thnu the males."' 'I'he small size of 

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

 times carried to an extreme degree), and their widely ditt'erent appear- 

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



Sume of the lower Crustaceans are able to proprigate their kind 

 nsexu.lly, and this will account for the extieme larity of the males: 

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

 Apus from twenty-one Idealities, anil amongst these he found only 

 319 males. Witii some olher forms (as Tanais and Cypris), as Fritz 

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

 bliorter-l.ved tha:i the females; and this would explain their scarcitv, 

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

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

 Diastyliilse and of Cypridina on the shores of Brazil; thus wit.i a 

 species in tlie latter genus, tj3 specimens caught the same day included 

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

 Slime unknown diiference in the liabits of the two sexes. With one 

 of the higher Brazilian crabs, mmely u (lelasimus, Fritz Miiller' 

 found the males t3 be more numerous than the females. According 

 to the large experience of Mr. U. Spence Bate, the iever?e seems \a 

 be the ease witu six common Briiiiih crabs, the names of which ho 

 has given me. 



The proportion of the sexes in relation to natunil 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 then: 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 Yelderslcy House informs me that one of his Arab mares, 

 though put seven times to different horses, produced stjven 

 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 

 fiimilies of short-horn cattle. Col. Marshall'* has recently found 

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



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



-espcct to this class. Prof. Thorell of ' Quarterly Journal of Science,' 



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

 18G9-70, part i. p. 205) speaks as if " ' IJeitrage zur Parthenogenesis,' 



female spiders were generally com- p. 174. 

 (Doner than the males. " ' The Todas," 1873, pp. 100 



« See, on this subject, Mi-. Ill, 194. 1&3. 



