Thus Mr. Trimen has described the pupae of the two forms as 

 differing, and Mr. Marshall considers that both are certainly 

 procryptic in colouring, that of sesamus being gilded and con- 

 cealed by its harmony with the yellow winter foliage, while 

 that of natalensis is dull brownish-black, with black patches 

 on the wings, and is protected among the dark withered leaves 

 of the moist summer. In one case he has bred the red form 

 from a gilded pupa, but never sesamus from a dark one. It 

 would be of great interest to ascertain whether these 

 pupae exhibit true seasonal differences, or whether, as seems 

 more probable, the mature larvae are susceptible to the 

 colours of their immediate environment, as has been 

 proved to be the case with those of several of the allied 

 Vanessidae. 



" Of still more importance is, the decision as to the cause 

 or causes of the seasonal differences of the imago. On this 

 question Mr. Marshall maintains that ' it at once becomes 

 evident that the directly exciting cause is a climatic one ' 

 {I.e., p. 37), and he argues that moisture, rather than tempera- 

 ture, supplies the efficient stimulus. The great want in the 

 matter is experimental inquiry on as extensive a scale as 

 possible, carried on over a large part of the year, so as to in 

 elude larvae and pupae, that in the ordinai-y course certainly 

 produce the blue form, as well as those that produce the red, 

 and those that, at intermediate times, are known to produce 

 both forms. 



" Concerning those last-mentioned, Mr. Marshall has shown 

 conclusively that the offspring of a single parent, brought up 

 under the same conditions, may belong to both forms ; in 

 fact, in his experiment already described, the summer form 

 emerged five days later {i.e., when the winter season was to 

 that extent advanced) than the winter form. This fact leads 

 us to contemplate the possibility that the change of form is 

 due to internal causes and independent of, although on the 

 whole synchronous with, the seasons. 



" And even if some exciting cause be proved to be necessary, 

 it is probable there are great differences in the internally 

 caused degree of susceptibility to stimulus in the two seasons, 

 while a mixed susceptibility exists in the intermediate period. 



