N0.566] SHORTER ARTICLES AND DISCUSSION 123 



per se. A few state that the atmosphere was "moist" or "dry," 

 but even then how moist or how dry is not usually mentioned 

 unless it is believed to be saturated or absolutely free from moist- 

 ure. It is clearly incumbent upon the one who makes such a criti- 

 cism to show, either by his own work or in a review of that of 

 others, that humidity is a factor of such importance that the 

 criticism is worth the making — especially since the point is so 

 self-evident and has been made in the past. The following notes 

 are an attempt to justify the preceding. 



The experiments of many workers show that when lepidop- 

 terous pupse are subjected to abnormal temperature part, at 

 least, of the adults which emerge differ from the normal. The 

 observations have usually been made on color changes, and 

 Fisher 2 especially has shown that warm conditions (36° to 41° C.) 

 produce the same or similar effects as do cold conditions (0° to 

 10° 0.), also that hot conditions (42° to 46° C.) produce effects 

 which are similar to those produced by freezing ( — 20° to 0° C). 

 Fisher apparently had no means of successfully controlling the 

 humidity but Tower 3 claims to have had this in his "Investiga- 

 tion of Evolution in Chrysomelid Beetles of the Genus Leptino- 

 tarsa" and he obtained similar results, stating them as follows: 



The result produced by either a higher or a lower temperature is the 

 development of a greater amount of pigmentation and a consequent me- 

 lanic tendency in variations. This stimulus in both directions to increased 

 I'ignimtation reaches a maximum between 5° and 7° C. deviation from 

 normal. Beyond these, as the temperature further deviates, there is 

 a rapid fall in melanism, first to the normal, and then to a condition 

 below normal, until a marked albinic tendency is found; and this de- 

 crease in pigmentation continues until the zero point is reached, be- 

 yond which no pigment whatever is produced. The zero point is 

 reached much sooner, however, in high-temperature experiments than 



Tower then gives the results of experiments in which all the 

 environmental conditions, except humidity, are "normal." 

 Normal humidity for Leptiiwtarsa decemlineata is taken as rang- 

 ing from 43 per cent, to saturation with an average of 74 per cent. 

 The humidity in various experiments ranges from 10 per cent, to 

 saturation. The lowest natural humidity of which I have seen 

 a record is 5 per cent. It occurred in Death Valley, California, 



2 See Archiv fur Eassen- und Gesellschafts-Biologie, 1907, IV, pp. 761- 

 793, for Fisher's statement concerning criticisms of his conclusions. 



3 Carnegie Institution of Washington, Publication No. 48, 1906. 



