7606 Notices of New Books. 



been developed and improved by processes which are assumed as the 

 means of organic modification. Mr. Darwin appears to look upon 

 instinct as parallel with any other quality essential to the existence of 

 the possessor, and like any mere physical advantage has been gradu- 

 ally developed by the process of natural selection. Referring to the 

 instincts of the honey bee, the individual which would construct its 

 cells of the greatest capacity, with the least amount of material, would 

 have an advantage over its fellows in storing honey for the winter, and 

 the power of manufacturing the beautifully perfected hexagonal con- 

 struction might therefore be graduall)'^ developed by the accumulated 

 inheritance of that half-mental experience we call instinct, through 

 those individuals that have become dominant from attaining to the 

 most perfect economy in the construction of the comb. If we look 

 upon instinct as merely the inherited experience of bygone generations 

 it may perhaps be admitted into the same category as the more strictly 

 physical qualities, which Mr. Darwin tells us have been developed by 

 natural selection ; he even enlists the existence of some instincts as 

 favourable to his theory, and says that those common to the widely 

 isolated species of the same genera distinctly point to genealogical 

 affinity. 



Another grave difficulty in the way of the theory of natural selection 

 occurs in the fact of the production, by some insects, of neuter, sterile 

 casts, or particular groups of isolated individuals, distinctin structure and 

 habits from the ordinary line of generation. It seems almost impossible 

 that these can have been produced by gradual modification, because 

 they leave no inheritance to gradually accumulate the deviation from 

 the generating line, and, furthermore, the whole amount of difference 

 is accumulated in a single generation, but Mr. Darwin says, on the 

 assumption that these sterile casts are of advantage to the social 

 economy of the species, the individuals tending to produce them would 

 become dominant and gradually accumulate the property of generating 

 the completely sterile neuter casts. 



The alleged fact of the fertility of the hybrids produced by the 

 crossing of varieties, and the sterility of those produced by the crossing 

 of species, would imply two serious difficulties ; first, an essential 

 difference between varieties and species, which Mr. Darwin says is 

 one only of measure ; and secondly, a natural provision for the main- 

 tenance of the individuality of species. Chapter VIIL, on the subject 

 of hybridism, is principally devoted to questioning the force of the 

 evidence that has been adduced in favour of an absolute difference 

 between the fertility of the oflspring of crossed varieties and crossed 



