temperature on the colouring of Lepidoptera. 43 



the 3rd and 25tli July, only one being a cripple. I have 

 failed to see any difference of appearance between the 

 two lots. I may add that I could not find any difference 

 in colouring produced in this species by the difference of 

 temperature between pupa3 kept at 80^, and emerging in 

 5 to 6 weeks, and pupse kept in the open air and emerging 

 in about 4 months. 



General speculations as to temperature effects. — Some of 

 the results seem attributable to the cause that a par- 

 ticular temperature is more conducive to health and 

 vigour than any other, and therefore may be expected to 

 produce larger size and greater intensity of coloration, 

 which, in insects of the colouring of those operated on 

 by me generally, but not always, means greater darkness. 

 The connection between "varieties" and "cripples" is 

 well known. A temperature of about 58° or 60° in 

 V. urticce seems to be the one most conducive to bright- 

 ness and intensity of colouring and marknig. And a 

 temperature of 47°, especially if long continued, seems 

 to stunt its size, as well as to deaden its brightness, and 

 to produce a large proportion of cripples. In B. quercus, 

 and still more in its var. calkmce, a temperature of 60° 

 appears more conducive to vigour than a higher one. 



But this is quite insufficient to account for all the 

 effects produced by temperature in the cases of V. urticce, 

 B. quercus (and callunce), C. caja, and E. autumnaria. 

 Apart from the changes of colouring that may be sup- 

 posed to be dependent on vigour, there seems in all these 

 species what may provisionally be called a direct* tendency 

 in the lower temperature to cause darkness, either by 

 obscuring the general colour or increasing the size and 

 intensity of the dark markings, or by some or all of these 

 combined. And in the seasonally dimorphic species, 

 such as the Selodas (and probably in falcataria also), the 

 intensity and darkness of coloration caused by tempera- 

 ture appear to be quite independent of health and vigour, 

 for those which have been forced, whether of the spring 

 or summer emergence, appear in every way as healthy 

 and well developed, and as thickly clothed with scales, 

 as those kept at the lower temperature. 



'■■'• In using this term I should have excluded from its application 

 such effects in the way of darkness as can be explained by Weiss- 

 mann's theory that the low temperatxu-e causes reversion to a 

 darker ancestral form: a subject adverted to by me in earlier 

 papers. 



