30 THE ZOOLOGIST. 



dividualism," and to be so nearly akin that they seek these 

 mates with mutual satisfaction and as much or nearly as much 

 avidity as they do their natural consorts. 



In the middle division C. the animals have so far receded 

 that hybrids of this class are harder to get. There seems to be 

 less attraction between the combining animals, and they have 

 often to be kept together, and away from their proper mates, 

 before they will copulate. 



In D. anyone with experience of Mule breeding will note the 

 general want of affection between the ass and the mare, or the 

 stallion and she ass. 



And in E. this mutual intolerance is perhaps somewhat more 

 apparent still. 



All this looks so remarkably gradual, so evident and simple, 

 that there appears no anomaly of any kind, except those which 

 the arbitrary (and changing) barriers of our classification 

 schemes erect. There are, however, a number of curious and 

 contradictory results obtained by plant hybridisations that are 

 difficult to understand ; they occur also, as Mr. Finn has 

 pointed out, in birds,* viz., that a hybrid that is hard to get, 

 Wood-Pigeon and Common Pigeon (and which we might expect 

 to class in group D. or E.), proves fertile, and, therefore, 

 apparently has to be included in group A. (I should like to see 

 this experiment repeated.) I do not think these aberrant results 

 (or as we think them aberrant) destroy the results which we get 

 in the above table, or the evidence which this brings forward of 

 a certain gradual tendency and law in hybridisation. These 

 graduating results, however, perhaps do not seem altogether so 

 amicable to the fascinating theory of evolution of species by 

 spontaneous variation or mutation, as they do to " indefinite " 

 variation. Darwin held it probable that species arise but rarely 

 violently in this way (which is suggestive of the theory of Cuvier 

 and others of the separate creation of species), but generally by 

 the slowest and most gradual changes, as we will notice later on. 

 Still this debatable point has never been settled. One must 

 bear in mind, however, before definitely stating, as some may 

 do, that these anomalies destroy our more general results, that 

 in breeding with wild forms, environment or change of food 



* ' The Feathered World.' 



