No. 566] SHORTER ARTICLES AND DISCUSSION 127 



not only the color and form of scales but also the form of an- 

 tennas, legs and other body parts of Lepidoptera. He exposed 

 the pupae to 42.5° C, humidity not given; 38° to 39° C. and 42° 

 to 43° C, relative humidity 80; 8° C., "high humidity"; 0° C, 

 "very high humidity"; —7.5 to 5° C, relative humidity 80-90 

 and 50; and — 11° C, humidity not given. For the most part 

 the humidity was high and probably had much to do with the 

 results, but we can not be certain. 



All the experiments just considered were made upon pupae. 

 It should be remembered that only about one fourth of the weight 

 of lepidopterous pupa* consists of solids, and that the only way 

 they can replace fluids lost by evaporation is by chemical changes 

 in these solids. It is probable that they do so to some extent, 

 although this has not been accurately determined. It is known 

 that under normal conditions pupae lose in weight and the per- 

 centage of solids increases. Naturally, a change in the humidity 

 of the surrounding air would modify this physiological process 

 and it is difficult to believe that it has not quite as much effect as 

 changes in temperature, the humidity remaining the same. It 

 is easy to see that, if the air is made more absorptive or less ab- 

 sorptive either by the temperature changes themselves or by other 

 means, and then the physiological activities are slowed or quick- 

 ened by temperature changes, the effects will be much greater 

 and might easily pass as due entirely to the temperature changes. 



The species which have wet and dry season forms in regions 

 where the temperature is fairly constant throughout the year, as 

 well as the tendency for the animals of moist regions to be mel- 

 anic and of arid regions to be light colored, speak for the impor- 

 tant influence of humidity. But there is another point in 

 distribution to be considered. The study of distribution was 

 long, and still is, largely an effort to get the ranges of animals 

 and plants to fit isotherms. When yearly averages do not work, 

 winter minima or summer maxima or accumulated temperatures 

 are tried. The success which often attends these efforts shows 

 that man is very ingenious and also that temperature is really 

 one of the controlling factors, but it does not show that it is the 

 only factor or, in fact, that it has any direct influence. 



The areas of grassland and forest in North America cut across 

 isotherms as though they were merely political boundaries but 

 Transeau* has shown that if we plot the ratio of temperature to 



Amer. Nat., XXXIX, pp. 875-889, 1905. 



