m FlitST CROSSES AND OF HYBRIDS. 277 



/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 luxuriance. In both 

 cases the sterility occurs in various degrees ; in both, the 

 male element is the most liable to be affected; but some- 

 times 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 unnatural conditions; and whole groups of species 

 tend to produce sterile hybrids. On the other hand, one 

 species in a group will sometimes resist great changes of 

 conditions with unimpaired fertility ; and certain species in 

 a group will produce unusually fertile hybrids. No one can 

 tell till he tries, whether any particular animal will breed 

 under confinement, or any exotic plant seed freely under 

 culture; nor can he tell till he tries, whether any two 

 species of a genus will produce more or less sterile hybrids. 

 Lastly, when organic beings are placed during several gen- 

 erations under conditions not natural to them, they are 

 extremely liable to vary, which seems to be partly due to 

 their reproductive systems having been specially affected, 

 though in a lesser degree than when sterility ensues. So it 

 is with hybrids, for their offspring in successive generations 

 are eminently liable to vary, as every experimentalist has 

 observed. 



Thus we see that when organic beings are placed under 

 new and unnatural conditions, and when hybrids are pro- 

 duced by the unnatural crossing of two species, the repro- 

 ductive system, independently of the general state of health, 

 is affected in a very similar manner. In the one case, 

 the conditions of life have been disturbed, though often 

 in so slight a degree as to be inappreciable by us ; in the 

 other case, or that of hybrids, the external conditions have 

 remained the same, but the organization has been disturbed 

 by two distinct structures and constitutions, including 

 of course the reproductive systems, having been blended 

 into one. For it is scarcely possible that two organizations 

 should be compounded into one, without some disturbance 

 occurring in the development, or periodical action, or mutual 

 relations of the different parts and organs one to another or 

 to the conditions of life. When hybrids are able to breed 

 inter se, they transmit to their offspring from generation to 

 generation the same compounded organization, and hence we 

 need not be surprised that their sterility, though in some 



