374 , EwART — Variation : Gernwial and Environmental. 



particular environment, but in both cases there will be danger from the " swamping 

 effects of intercrossing." This danger will obviously be avoided if, when the new 

 and old varieties intei'cross, the offspring are either the image of the old or of the 

 new. If, in addition to an inability to produce intermediate forms, the new variety 

 is better adapted for the environment, it will survive even if its increase is at first 

 slow. 



4. Tlie offspring may combine, almost unimpaired, the more striking characters 

 of both breeds. Though the engrafting of the characters of one breed on another 

 may not be common, it certainly occurs. Two instances may be mentioned : 

 (1) In crossing a barb with an " owl," the frill of the owl on two separate occasions 

 made its ajjpearance on the offspring, one of which, from a fancier's point of 

 view, was, apart from its frill, a better barb than its pure-bi"ed barb parent ; 

 (2J In crossing a home-made Himalaya rabbit with an Angora, two young were 

 obtained, having the long hair of the Angora and the dark markings of the 

 Himalaya. That it is possible to roll two races or breeds into one is extremely 

 interesting and suggestive. Darwin supposed that when two distinctive types 

 were crossed, reversion followed from a kind of antagonism, i.e. from the germ-plasm 

 of one type opposing and neutx'alizing the germ-plasm of the other. What 

 happens when intercrossing is jjractised evidently largely depends on the pre- 

 potency of the parents, or, to be more accurate, on the prepotency of the germ- 

 cells lodged in the parents. This prepotency may again depend partly on the 

 inheritance, and partly on the environment from the outset of development uj) to 

 the time when maturity is well established. When the characters of one race are 

 engrafted on those of another, it is not, I believe, because there is an absence 

 of antagonism ; it is rather that in both germ-cells there is almost sufficient energy 

 to give rise, unaided, to a new individual. The Skewbald pony producing a foal 

 as like herself as if it had grown from a cutting or bud, supports this view, but 

 still stronger support is afforded by the recent work of Yves Delage,* who has 

 succeeded in obtaining larval echinoderms, worms, and molluscs by fertilizing 

 enucleated eggs. If in nature, two distinct types occasionally blend, it will be 

 evident that the rate of evolution, even without the help of occasional " sports" 

 may have been infinitely more rapid than Darwin and many of his followers 

 imagined. If the blending of external characters is possible, it may almost be 

 taken for granted that the blending of mental characters is also possible. I find 

 when my zebra hybrids are intensely striped, they exhibit practically all the 

 mental traits of their zebra sire. This might, perhaps, have been anticipated, for 

 the epidermis and its appendages and the central nervous system are akin in their 

 origin. Hence, from the fact that distinctive epidermic characters of one vai-iety 

 of pigeons can be engrafted on quite a different variety, it may be inferred that, 



* Archives de Zoologie Experimentale, Oct., 1899. 



