66 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



incapable of exercising their sexual functions, &c. In this 

 respect the most interesting examples are those of the influence 

 of deficient nutrition on the larva forms or on the conditions of 

 development. Unfortunately next to nothing reliable is known 

 on this subject, and it is much to be wished that the various 

 observations that have been accidentally made and interpreted 

 ' to taste ' should be made the starting-point for actual experi- 

 mental investigations on this question. I will here mention 

 a few of what seem to be the most trustworthy of these. Mr. 

 T. Gentry, of Philadelphia, has shown that the larvae of a moth 

 Acronycta sp. entirely lose the habit of spinning a cocoon 

 before assuming the pupa state when their food is insufficient, 

 and that both the pupas and moths are then smaller. The 

 observations independently made on the Hydroid Polyps by 

 Hincks, Allman, and Schneider are highly interesting. Ac- 

 cording to these, in the first place a Medusa of the group of 

 the Hydroida can be induced by lack of nourishment to assume 

 the polyp-form, i.e. the larva form of the species. Secondly, 

 the hydroids of the h igher Discoid Medusae as Medusa chrysaora 

 and others produce much fewer Medusae in confinement than 

 in the open sea ; and this has been accounted for, somewhat 

 hastily, by the assumption that deficiency of food is the cause. 

 Experimental proof of the accuracy of this hypothesis has not, 

 however, been adduced. 



The quality of the food, next to the quantity, exerts a direct 

 modifying influence which in many cases exhibits itself in the 

 organs most nearly interested those, namely, of digestion 

 though others may become subject to it. More rarely the whole 

 size attained by the animal may be conspicuously affected by 

 it. But we possess only a few trustworthy observations on this 

 point, interesting as it is, and still fewer available physiological 

 experiments, though such are indispensable. The lack of 

 materials on this subject renders it necessary to discuss it briefly 

 here. 



In the first instance the statements of Wallace and others 

 as to the influence of food on coloration must be mentioned, since 

 Seidlitz in his various works attributes great importance to 

 them, although, as it seems to me, he assumes something ho be 



