80 THE ORIGIN OF SPECIES 



out any obvious cause, apparently from mere inability 

 to live"; so that from the 500 eggs only twelve chickens 

 were reared. With plants, hybridized embryos probably 

 often perish in a like manner; at least it is known that 

 hybrids raised from very distinct species are sometimes 

 weak and dwarfed, and perish at an early age; of which 

 fact Max Wichura has recently given some striking cases 

 with hybrid willows. It may be here worth noticing that 

 in some cases of parthenogenesis the embryos within the 

 eggs of silk moths which had not been fertilized pass 

 through their early stages of development and then perish 

 like the embryos produced by a cross between distinct 

 species. Until becoming acquainted with these facts, I 

 was unwilling to believe in the frequent early death of 

 hybrid embryos; for hybrids, when once born, are gen- 

 erally 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 live, they are gen- 

 erally placed under suitable conditions of life. But a 

 hybrid partakes of only half of the nature and constitu- 

 tion of its mother; it may therefore before birth, as long 

 as it is nourished within its mother's womb, or within 

 the egg or seed produced by the mother, 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 are eminently sensitive to injurious 

 or unnatural conditions of lite. But after all, the cause 

 more probably lies in some imperfection in the original 

 act of impregnation, causing the embrj'-o to be imper- 

 fectly developed, rather than in the conditions to which 

 it is subsequently exposed. 



