354 THE INFLUENCE OF LIVING SURROUNDINGS. 



Among insects, however, there are several species known which 

 readily breed together and produce hybrid offspring ; thus a 

 cross has been produced between the larger and smaller peacock 

 moths and between the willow and the poplar hawk-moths. I 

 have intentionally mentioned here only some of the more recent 

 cases (there is a mass of well-established older examples which 

 may be found briefly enumerated in the fourth edition of Claus's 

 ' Lehrbuch dor Zoologie '). m 



This must suffice ; the fact that two different species can 

 unite and be fertile must be regarded as established, for in most 

 of the cases here enumerated the individuals breeding together 

 stand so far apart in the systematic scale that no systematic 

 zoologist not even the most virulent anti- Darwinian could 

 venture to assert that they were only varieties of one and the 

 same species. 



However, to deprive these numerous instances of hybridi- 

 sation of any univei-sal application and value, it is further 

 asserted that the newly originated hybrid forms are always, or 

 almost always, sterile. But even this statement must be 

 declared to be inaccurate in its naked and literal form. The 

 race of the Leporiclae is, as is well known, perfectly fertile, and 

 has produced other cross-breeds with both the rabbit and the 

 hare. Hybrids between the dog and jackal or between the dog 

 and wolf remain fertile for many generations ; those of Phasia- 

 nus colckicus and torquatus are perfectly fertile; so are the 

 well-known hybrid geese, and those between Cervus vaginalis 

 and Cervus Reevesii ; a female mule in the Jardin d'Acclima- 

 tation at Paris has produced two foals to a horse and two to 

 an ass ; in the Zoological Gardens (London), a hybrid female of 

 Bos indicus has had young by a male of Bos frontalis. Newton 

 states that a hybrid female between the common duck and Anas 

 boschas proved fertile with a male Mareca peneloj)e, and I have 

 no doubt that many similar cases have escaped my notice. 

 The infertility of hybrid races is certainly not a universal law, 

 for besides those cases which are always, or under certain cir- 

 cumstances, infertile, we meet with others, as we have seen, 

 not less numerous, of which the undiminished fertility is un- 

 doubtedly established by reliable observers. We may conse- 



