AMERICAN ZOOLOGISTS AND EVOLUTION. 813 



chances for destruction of the summer eggs in the dry and often dusty- 

 soil are so numerous that only the most prolific species can maintain 

 themselves under such conditions. 



" Further, the marshes and shallower lakes are the favorite breeding- 

 grounds of fishes, which migrate to them in spawning-time, if pos- 

 sible, and it is from the entomostraca found here that most young fishes 

 get their eai'liest food-supplies a danger from which the deep-water 

 species are measurably free. Not only is a high reproductive power 

 therefore rendered unnecessary among the latter by their freedom 

 from many dangers to which the shallow- water species are exposed, 

 but in view of the relatively small amount of food available for them, 

 a high rate of multiplication would be a positive injury, and could 

 result only in wholesale starvation." 



The effect of birds on insect-life has engaged the attention of the 

 same author.* His inquiry was to ascertain whether birds originated 

 any oscillations in the numerical proportion of insects upon which they 

 feed. Many interesting facts are given which space forbids quoting. 



A number of contributions have been made on the influence of envi- 

 ronment and on geographical variation, to some of which reference 

 must be made. Prof essor Alpheus Hyatt f bears unequivocal testimony 

 to the derivative theory, and recognizes clearly the influence of exter- 

 nal surroundings in a memoir on the cephalopods, when in stating the 

 law of organic equivalence he says : " The action of physical changes 

 takes effect upon the irritable organism, which necessarily responds to 

 external stimulants by an internal reaction or effort. This action from 

 within upon the parts of the organism modifies their hereditary forms by 

 the production of new growths or changes which are, therefore, adapted 

 to the conditions of the habitat or the physical agents and forces from 

 which they directly or indirectly originate " ; or, slightly changing this 

 interpretation in accordance with the same facts, each individual is more 

 or less susceptible to the action of physical influences and those which 

 respond most quickly to these influences, come more promptly in harmony 

 with their environment, which is natural selection pure and simple. 



Mr. Charles Morris, J in a series of papers on " Organic Physics " 

 and the "Polar Organization of Animals," presents many new and 

 suggestive thoughts on the physico-chemical action in life and devel- 

 opment. He concludes that " there are inherent in the germ energies 

 and tendencies, chemical, molecular, or whatever we choose to call 

 them, adapted to the complete unfoldment of the typical form. But, 

 as appears evident, their operation can be checked by influences from 

 external nature. There is a struggle between these contact influences 

 and the innate organic tendencies." 



* " American Naturalist," vol. xvii, p. 671. 



f " Proceedings of the American Associated Antiquarian Society," vol. xxxii, p. 323. 



\ " American Naturalist," vol. xvii, p. 486. 



[To be continued.] 



