THE PUPA OB CHRYSALIS 47 



April, and may be found in numbers throughout the winter, at- 

 tached to the walls and fences of kitchen and market gardens. 



If, then, the pupae of the same species are so influenced by the 

 temperatures of the seasons, can we limit or prolong the period 

 of quiescence by subjecting them to high or low temperatures 

 artificially produced "? Most certainly we can ; and every practical 

 entomologist knows how to obtain the perfect butterflies and 

 moths of certain species long before their appointed times, or, 

 if he desires it, to compel them to remain in their dormant stage 

 long after the natural period has terminated. 



Sometimes an enthusiastic insect hunter obtains a large nuujber 

 of what we may term ' winter pupae,' by collecting and breeding 

 various species. He also anticipates a number of successful captures 

 of perfect insects during the following summer. Thus, fi-om two 

 distinct sources, he obtains a goodly assortment of butterflies and 

 moths, the setting, preserving, and arranging of which entails an 

 immense amount of home work. 



Under such circiimstances he will sometunes endeavour to cause 

 some of his pupae to emerge before their accustomed time, so that he 

 may get some of his insects ' on the boards ' before his field work 

 is in firll swing, and so avoid a rush, or prevent the loss of insects 

 that will be spoiled before he has time to take them in hand. 



This process of hurrying up his pupae he calls ' forcing,' and 

 simply consists in keeping them for a time in a warm room or hot- 

 house where the high temperature is pretty constant. 



On the other hand, the entomologist may desire to try the effect 

 of a continued loiv temperature on his pupae. This he can do by 

 placing his pupte in an ice house. Such experiments have often 

 been performed, and the results are very interesting. In some 

 cases the emergence of the perfect insect has been delayed for many 

 months, and even 3-ears ; and then, after an exposure to a normal 

 temperature lasting only a week or two, the winged insect has 

 made its appearance just as if nothing unusual had happened. 



Such are the effects of extreme temperatures on the duration 

 of the chrvi-alis state ; and we naturally infer, from such results, 

 that the pupa under natural conditions is influenced, though in a 

 lesser degree, by the variations experienced with the seasons, 

 especially in such a fickle climate as our own. 



The msect hunter has always to bear this in mind, and particu- 

 larly so when he sets out on a search for certain desired species. 

 Suppose, for example, he has set his mind on the capture of a 



