DARWIN AND HIS CRITICS 67 



no apparent reason exists. The sterile male 

 hybrids between the pheasant and common fowl 

 take great delight in sitting, whenever they can 

 find a nest of eggs unoccupied by the hen.* A 

 more important fact is that though hybrids can 

 be obtained between two allied hawk-moths 

 (Smerinthus Ocellatus and A?. Populi), the sexes 

 are nearly always mixed, as well as the species. 

 The normal larvas discharge either a white or a 

 yellow fluid when touched, according to sex ; 

 but the hybrid larvae discharge both.f Mr. 

 Jenner Weir informs me that the mammas are 

 unusually large in male mules in Spain. As the 

 sexes become very gradually separated as we 

 ascend in the animate scale, it appears highly 

 probable that reversion may play some part in 

 this tendency to hermaphroditism in hybrids. 

 It may here be suggested that some breeds 

 of cattle, among which hermaphroditism is 

 exceedingly frequent, may have sprung to a 

 greater extent than others, from a mixture of 

 several wild species. 



Having now briefly glanced at some of the 



* Darwin, "Animals and Plants under Domestication," vol. ii. p. 52. 

 f Trans. Ent. Soc. Lond. vol. iii, pp. 193202. 



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