424 STERILITY OP HYBRIDS. 



for exudation from the organism, for reproductive 

 purposes. 



An individual, with all the characters of its species 

 fully and proportionately developed, may be likened 

 to a perfect, symmetrically-formed "burning lens," 

 with all of the rays, which pass through it, determin- 

 ing to the center. An individual, belonging to a di- 

 vergent variety deficient in some of the characters of 

 its species, may be likened to the same lens, but 

 notched, and with a ragged edge. The force, therein 

 coursing, does but imperfectly converge ; and the degree 

 of the imperfection determines whether the effective 

 concentration of the rays may at all be attained. If 

 the imperfection be very great, the said effect will be 

 wholly precluded. So, if the reduction of characters, 

 in an individual, be great, the reproductive power is 

 wholly absent, upon interbreeding with another indi- 

 vidual similarly deficient. On the other hand, a hy- 

 brid, — the product of a cross between two distinct 

 species, — may be likened to a glass, made in the simili- 

 tude of a "burning lens" with two foci. The forces, 

 contained therein, — which would be competent to the 

 production of a given effect, were the rays converged 

 to one point, — are, as there are two foci, rendered 

 wholly inoperative for such a result. So ; the hybrid 

 would be fertile, were the point, or points, to which 

 the influence of its aggregate determines, susceptible 

 of being exuded. But, as there is but one point, viz., 

 the site of the reproductive organs, where the structure 

 contemplates exudation; and as the influence of the 

 aggregate is not concentrated there, the hybrid needs 



