24 Experimeiital Zoology 



temperature a lighter one, this is not invariably the rule, 

 as seen in certain dimorphic forms. Thus, in Lythria rotaria 

 the butterfly that hatches in the spring (from over-wintering 

 pupae) is darker than the summer type (the second generation, 

 variety L. purpuraria). On the other hand, Vanessa levana 

 (also from over- wintering pupas) is lighter than the summer 

 variety, V. prorsa. A lower temperature does not therefore 

 always produce darker colors and a higher temperature lighter 

 ones, although this is the general rule, but the reaction depends 

 also on the nature of the organism. 



In these experiments with butterflies the more conspicuous 

 result is the change in color ; but it should not be forgotten that 

 changes in size also often occur, and even constant changes in the 

 shape of the wings have been observed, the outline of the wing in 

 some cases being quite dift'erent from that of the normal animal. 



Effect of Temperature on Caterpillars 



Standfuss has shown that by rearing caterpillars at a higher 

 temperature (2o°-25° C.) than normal, the characters of the 

 moths may be affected.^ Changes in the shape of the wings 

 are sometimes caused in this way. The color is also altered 

 to some extent. The most constant change, however, is in 

 the size. Standfuss gives the following rule: ''The more 

 the feeding period of the caterpillar is shortened by raising the 

 temperature the smaller the butterflies. Lasiocampa quercifolia, 

 for example, had its weight decreased in this way to one 

 seventh of the normal. On the other hand, if the time of feed- 

 ing (or in other words the time of the caterpillar stage) is not, 

 or only very sHghtly, shortened, despite the higher temperature, 

 there is an increase in size, which in the case of Arctia fasceata 

 may be as much as half again the entire normal weight." 



Standfuss points out that results similar to these are found 

 in nature where the size of certain forms appears to be connected 

 with the time of year at which the pupae appear. Species 



^ Merrifield also has made observation on the effects of temperature on 

 caterpillars. 



