38 Experimental Zoology 
(2) iron albuminate (officinal solution: 4 parts metallic iron to 
tooo water); (3) argonin silver casein (5 per cent); (4) sugar; 
(5) lupulin; (6) capsicum; (7) morphine (1 per cent); (8)atropin 
(1 per cent). 
The iron and the silver compounds by exciting hunger 
tended to produce larger forms. The largest butterflies came 
from caterpillars fed with argonin silver casein and the smallest 
from those given morphine with their food. The younger the 
caterpillars, when the experiment began, the better the results. 
Darkening of the ground color of the wings was found after 
argonin and morphine. Also much red was present. Capsi- 
cum also gave a dark background. The color was strongly 
developed after iron, sugar, and lupulin. The markings were 
affected in much the same way as by cold and warmth. Re- 
duction of the black or of the blue flecks occurred in some 
cases. 
Pure Oxygen. — Pupe kept in pure oxygen produced in the 
usual time butterflies normally colored and marked. Young 
caterpillars kept in oxygen took food for only one day, wandered 
about the next day, and died on the third or fourth day. The 
moist atmosphere rather than the oxygen may have been respon- 
sible for the early death of the caterpillars. 
The Influence of Humidity on the Characters of Moths and 
Butterflies 
Humidity is also supposed to have an effect on the coloration 
of butterflies. Marshall thinks that in the Transvaal, where a 
dry and a wet season alternate, as do summer and winter in 
northern climates, the seasonal dimorphism of certain butterflies 
is the direct result of the effects of moisture and of dryness, in 
the same way that cold and heat cause the seasonal dimor- 
phism of northern species. Similar results have been described 
by Doherty for Melanites leda of India. The differences fol- 
low the dry and the wet seasons. Pictet has shown that 
effects of this kind can be artificially produced in certain Eu- 
ropean species. Moisture on the leaves produces great mortality 
