122 Mr. Paget, [April 8, 



portion or season of a year, an independence of external conditions 

 appears less evident. The higher organisms, chiefly by reason of their 

 having in themselves the power of generating heat, may manifest their 

 own time-laws with comparatively little disturbance from without. 

 But in the vegetable world, and in the lower animals, the organic 

 processes are, for the most part, suspended during part of the year, 

 for want, chiefly, of the heat which is a necessary condition of their 

 activity, and the variations of which, for the rest of the year, very 

 greatly affect their rate. Yet even in these, there appear sufficient 

 indications that the times in which the processes of organic life are 

 accomplished depend, essentially, on the specific properties of the 

 several organisms themselves. 



Thus, under the same external conditions, each species observes a 

 proper rate of its own. All the plants, for example, of a given locality 

 are subject to the same temperature, and other seasonal conditions ; 

 but their rates of living, like those of various eggs placed in the same 

 heat, are different ; each reaches the chief events of its life at a certain 

 period of the year. Variations of the seasons may affect all of them ; 

 but their method of succession is not thereby changed ; they observe 

 the same proportions in the times severally required for their organic 

 processes ; and this unaltering proportion indicates a time-rate specific 

 for each, though equally variable in all. 



Moreover, among plants, there are numerous examples of varieties, 

 which differ from the general characters of their species only, or chiefly, 

 in regard to the times at which their vital processes are accomplished. 

 Such are the variations that are known as " late," and " early," among 

 flowers or fruits ; of which some may be propagated by seeds. 

 [Specimens were shown from two horse-chesnuts growing opposite to 

 one another by the great gate of the Kew Gardens, of which one is, 

 every year, three weeks earlier than the other, in all the processes of 

 its life ; and of varieties of Erythronium Dens Canis, from the same 

 gardens, the plants of which, growing side by side in the same bed, 

 always present a similar difference in their times of flowering, &c,, 

 though in all other respects alike.] It would be difliicult to imaginie a 

 variety thus marked only by a peculiarity in rate of living, if tempera- 

 ture, or the influence of the seasons, alone determined the rate of life 

 in the species. The simplest explanation seemed to be that, as there 

 may be varieties in size and number of organs, and almost all the other 

 properties of a species, which together make up its specific character, 

 so there may be also varieties in regard to that time-rate of the pro- 

 cesses of organic life which, even by this variability, is indicated as 

 essentially dependent on the properties of the organism itself. 



Again, there are some species in which there seems to exist a 

 singular independence of external conditions. Instances of this are 

 found in the Eriogaster lanestris, and the other moths mentioned by 

 Kirby and Spence. If pupae, formed in June or July, be " selected 

 of the same size, and exposed to the same temperature, the greater 

 number of them will disclose the perfect insect in the February follow- 

 ing ; some not till the February of the year ensuing, and the remainder 



