Chap. VIU. SUMMARY. 263 



through selection. Consequently, sudden reversions to the 

 perfect character of either parent would be much more likely 

 to occur with mono-rels, Avhicli are descended from varieties 

 often sudd(Mily produced and semi-monstrous in character, than 

 with hvbrids, which are descended from species slowly and 

 naturally produced. On the whole, I entirely agree witli Dr. 

 Prosper Lucas, who, after arranging an enormous body of facts 

 with respect to animals, comes to the conclusion that the laws 

 of resemblance of the child to its parents are the same, whether 

 the two parents dilTer little or nmch from each other, namely 

 in the imion of individuals of the same variety, or of different 

 varieties, or of distinct species. 



Independently of the question of fertility and sterility, in 

 all other respects there seems to be a general and close simi- 

 larity in the offspring of crossed species, and of crossed vari- 

 eties. If we look at species as having been specially created, 

 an'd at varieties as having been produced by secondary laws, 

 this similarity would be an astonishing fact. But it harmo- 

 nizes perfectly with the view that there is no essential dis- 

 tinction l^etwcen species and varieties. 



Summary of Chapter. 



First crosses between forms sufficiently distinct to be ranked 

 as species, and their hybrids, are very generally but not univer- 

 sally sterile. The sterility is of all degrees, and is often so 

 slight that the most careful experimentalists have arrived at 

 diametrically ojiposite conclusions in ranking forms by this 

 test. The sterility is innately variable in individuals of the 

 same species, and is eminently susceptible to the action of 

 favorable and imfavorable conditions. The degree of sterility 

 does not strictly follow systematic affinity, but is governed by 

 several curious and complex laws. It is generally different, 

 and sometimes widely different, in reciprocal crosses between 

 tlie same two species. It is not always equal in degree in a 

 first cross and in the hybrids produced from this cross. 



In the same manner as in grafting trees, the capacity of one 

 species or variety to take on another, is incidental on differ- 

 ences, generally of an unknown nature, in their vegetative sys- 

 tems, so in crossing, the greater or less facility of one species 

 to unite with another is incidental on imknown differences in 

 their reproductive systems. There is no more reaiion to think 

 that species have been specially endowed with various degrees 



