The Influence of External Conditions 



amongst the young caterpillars, but while the moths may be 

 small their markings show no variations. On the other hand, 

 although the fully formed caterpillars better resist the effects 

 of moisture, aberrations in the color are produced. Thus when 

 the caterpillars of Vanessa urticae were fed for 8 to 10 days- 

 on leaves kept constantly wet, changes in the markings of the 

 butterflies were produced. Similar results were brought about 

 in Vanessa polychloros and in Hybernia defoliaria. In Ocne- 

 ria dispar variations were induced in the first generation, but 

 disappeared in the second, owing, Pictet thinks, to the cater- 

 pillars having adjusted themselves to the change, in the same 

 way as they do to changes in their food. The variations in- 

 duced in the first generation are very much like those pro- 

 duced by esparcette and dandelion, especially in respect to the 

 males, and these plants contain a great deal of water in their 

 tissues. 



A fine spray of water at ordinary temperatures was con- 

 stantly applied for 36 to 48 hours to caterpillars of Vanessa 

 urticae that had suspended themselves preparatory to changing 

 into chrysalids. A marked effect was produced on the but- 

 terfly, a yellow band appearing across both fore and hind 

 wings. The blue spots became gray or violet, and the border 

 of the wings was clear. The variation resembles the variety 

 polaris of this butterfly. 



Humidity also acts on the chrysalid's stage, causing aberra- 

 tions in a number of moths and butterflies. If the chrysalids 

 are kept moist at a warm temperature, 30 to 35 C., very little 

 effect is produced, because the development is so much has- 

 tened that the chrysalids pass through the critical stages be- 

 fore the protecting waxy covering is worn away. But if the 

 chrysalids are kept cool while the moisture is applied, the effects 

 are much more marked ; for now the development is so much 

 delayed that the water has time to penetrate the protecting coat 

 and affect the critical stages. 



