CROSSING AND CLOSE-INTERBREEDING. 229 



which the offspring's fertility and constitutional vigor 

 would be affected, would be proportionate, simply, to 

 the small amount of tissue, which was wanting in the 

 structure of the eye, — which effect would be, prac- 

 tically, nil, even if the offspring and their descendants 

 interbred, brother and sister, for thousands of genera- 

 tions. 



A long catalogue could be given, of all sorts of 

 evils, in parts,- which are augmented in close-inter- 

 breeding ; but, whose effect is, of itself, little upon the 

 coordination of the whole; viz., cerebral affections, apo- 

 plexy, epilepsy, insanity, gout, consumption, asthma, 

 stone in the bladder, amaurosis, hypermetropia or 

 morbid long sight, myopia or short sight ; and, in 

 horses, for instance, ring-bones, curbs, splints, spavin, 

 founder, roaring, or broken and thick wind, melarosis 

 and blindness. 



Contradistinguished from these effects upon the 

 parts themselves, are the effects upon the aggregate ; 

 which Darwin cannot explain. They are lessened 

 fertility, sterility, loss of constitutional vigor, and a 

 general breaking up of the whole constitution. 



A man may have all of the specific diseases, to which 

 flesh is heir; yet, if he be otherwise proportionately de- 

 veloped, in all the characters of his species, he, and his 

 descendants, may go on, for many generations, inter- 

 breeding as close as did the Ptolemies, and remain of 

 undiminished fertility. The impairment of the balance, 

 would be in proportion only to the amount of tissue 

 destroyed, in the parts so affected, and not to the 



degree of the diseases' ordinary, baneful influence. 

 20* 



