The Influence of External Conditions 39 
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 
urtice 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. 
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