TJie Evidence from Hybrids. 127 



ants of a common ancestral form,, from which they 

 inherit all that they have in common,, while the distinc- 

 tive peculiarities which distinguish them from each other 

 are more recently acquired. 



According to our hypothesis the ovum transmits 

 established characteristics, while the cells which have 

 recently varied in the body of the male transmit gem- 

 mules. 



If, then, we select two allied species or varieties and 

 cross the male of one with the female of the other, and 

 then, reversing the process, cross the female of the first 

 form with the male of the second, we should expect to 

 find, in many cases, a difference in the offspring. Where 

 the male of species or variety A is crossed with the 

 female of B, the offspring will inherit from its mother 

 the common characteristics of both parents, and it will 

 also receive from its father gemmules from those cells 

 which have recently varied in the species A. The cor- 

 responding cells of its body will therefore be hybrids, 

 and will bear a closer resemblance than the other parts 

 of its body to the species A. That is, the hybrid will 

 share, to some extent, the peculiarities which are distinc- 

 tive of the species A as compared with B. The offspring 

 of the opposite cross will, on the other hand, join, more 

 or less perfectly, to the common race characteristics, 

 some of the distinctive peculiarities of the species A 

 produced in it by the hybridization of the cells of its 

 body by gemmules received from its father. 



Reciprocal crosses between the horse and the ass have 

 been reared for domestic purposes for ages, and Huxley 

 gives the following interesting account of the result: 



" The offspring of the ass and the horse, or rather of 

 the he-ass and the mare, is what is called a mule; and, 

 on the other hand, the offspring of the stallion and the 



