HYBRIDISM 237 



developed, and then perish at an early period. This 

 latter alternative has not been sufficiently attended 

 to ; but I believe, from observations communicated to 

 me by Mr. Hewitt, who has had great experience in 

 hybridising gallinaceous birds, that the early death of 

 the embryo is a very frequent cause of sterility in first 

 crosses. I was at first very unwilling to believe in 

 this view ; as hybrids, when once born, are generally 

 healthy and long-lived, as we see in the case of the 

 common mule. Hybrids, however, are differently cir- 

 cumstanced before and after birth : when born and 

 living in a country where their two parents can live, 

 they are generally placed under suitable conditions of 

 life. But a hybrid partakes of only half of the nature 

 and constitution of its mother, and therefore before 

 birth, as long as it is nourished within its mother's 

 womb or within the egg or seed produced by the 

 mother, it may be exposed to conditions in some degree 

 unsuitable, and consequently be liable to perish at an 

 early period ; more especially as all very young beings 

 seem eminently sensitive to injurious or unnatural con- 

 ditions of life. 



In regard to the sterility of hybrids, in which the 

 sexual elements are imperfectly developed, the case is 

 very different. I have more than once alluded to a large 

 body of facts, which I have collected, showing that 

 when animals and plants are removed from their 

 natural conditions, they are extremely liable to have 

 their reproductive systems seriously affected. This, in 

 fact, is the great bar to the domestication of animals. 

 Between the sterility thus superinduced and that of 

 hybrids, there are many points of similarity. In both 

 cases the sterility is independent of general health, and 

 is often accompanied by excess of size or great luxuri- 

 ance. In both cases, the sterility occurs in various 

 degrees ; in both, the male element is the most liable 

 to be affected ; but sometimes the female more than the 

 male. In both, the tendency goes to a certain extent 

 with systematic affinity, for whole groups of animals 

 and plants are rendered impotent by the same un- 



