On the Hybridising of Ducks. 253 



concerned with the greater number of species, but certain 

 exceptions obtain, amongst which we may mention some of 

 the Game Birds and Pigeons. This fertility or infertility 

 does not seem to follow any definite laws ; for instance crosses 

 between various species of the Bovidœ are generally fertile, 

 whilst among the Equidce there is no authentic instance of 

 such fertility. Among the Anatidœ trigen hybrids are by no 

 means unknown. M. Rogeron, in France, and Sir Richard 

 Graham, in this country, have obtained several such crosses, 

 but so far as I am aware they have not succeeded in raising 

 any young from them. My trigens prove, however, for the 

 most part (the dark form of P.M.S. trigen when bred inter se 

 being the only exception), perfectly fertile, either when bred 

 inter se, with digens or with pure species ; and the two 

 tetragens which I have been able to test 1 have also proved 

 quite fertile, both inter se and when crossed with a digen, so 

 that provided the stock does not become ' inbred ' it seems 

 probable that fertility between the various species of Anatidœ 

 is the rule rather than the exception. 



The five species with which my experiments have so far 

 been conducted and that have been united in a single 

 individual are very distinct ; in three of them the sexes are 

 different and the Drakes have an eclipse plumage, while 

 in the other two the sexes are alike and the eclipse plumage 

 is absent. They are inhabitants of the Palsearctic, Oriental, 

 Australian, and Ethiopian regions, and one of them, the 

 Pintail, is a member of a distinct genus, so that the objection 

 not unfrequently brought forward that fertile hybrids are, 

 as a rule, but varieties of one species, cannot in this case hold 

 good, and we must accept fertility between as many as five 

 species of the Anatidœ as an accomplished fact. 



II. Sex. 



The question of the sex of hybrids, more especially in 

 relation to their colour, is a point of extreme interest, but 

 one on which the facts at hand are insufficient to point to 

 any definite conclusions. 



1 I am now further able to add mv pentagen Drake, by whom I bave a fine 

 brood this year (1906). 



