Changes in the Life-cycle 313 



and the process appears to be reaching its limit, the individuals 

 may be rejuvenated by altering the composition of the solution 

 in which they live. They will then once more begin to divide 

 actively and start a new cycle or a new phase of the old cycle. 

 After a time under a constant environment their activity may 

 again begin to fall off, when a new change may rejuvenate them 

 once more. The precise effects produced are not known; for 

 it has been found that a change that affects rejuvenescence at 

 one time will not do so at another, and a different solution must 

 be used. The conclusion seems near at hand that conjugation 

 between individuals that have lived under different environments 

 may effect the same result in the same way as a change in the 

 environment itself. The problem may be, however, more com- 

 plicated than this. 



Influence of Food on the Life-cycle of Lepidoptera 



The caterpillars of moths and butterflies undergo a series of 

 moults as they grow larger, and during this time they consume 

 a very large amount of food. The length of the larval life 

 varies enormously. Thus according to Pictet the caterpillar 

 of Argynnis paphia takes 15 to 20 days from egg to chrysalis. 

 The caterpillars of the Vanessas take three to four weeks; 

 Ocneria dispar and Saturnia pavonia two and a half to three 

 months; Lasiocampa quercifolia eleven months (of which five 

 are in hibernation) ; Cossus cossus holds the record with a 

 larval life of two to three years. 



The pupa or chrysalid stages also have various periods. 

 Certain Vanessas take 12 to 18 days, and Ocneria dispar, Lasio- 

 campa quercifolia, and Cossus cossus take 18 to 28 days. Satur- 

 nia pavonia and S. pyri that become inclosed in the spring 

 generally pass two winters as chrysalids or pupae. The length of 

 life of these stages is, however, subject to great variation. The 

 amount of food obtainable is an important element in the result. 



Lasiocampa quercus hatches from the egg in the summer. 

 The larva remains active till about the first of November, hiber- 

 nates in the caterpillar stage until the end of April, when it 



