316 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
dates from June 3 to January 3. By raising these animals under 
constant temperature conditions and varying the strength of the 
nutrient solution, Woltereck proved that the relative size of body 
parts varied with the food. In Fig. 54 the percentages of head height 
to shell in length are plotted as abscissas and the numbers of indi- 
viduals as ordinates. Animals from three strengths of nutrient media 
were measured, the curves of those from the weaker, the medium and 
the richer media being shown at m,, m, and m, respectively. 
d) Moisture and plumage color. Beebe experimented with the 
pigeon, Scardafella inca. This species, as found in North and Central 
America, is very constant in color of plumage, but in the moist tropics 
+ 
30 35 40 45 50 55 60 65 70 
my, Me m3 
Fic. 54.—Schematic curves of head height in Hyalodaphnia as grown in 
media of three different food values. (From Babcock and Clausen, after 
Woltereck.) 
the following darker colored forms occur: in Honduras, dialeucos; in 
Venezuela, ridgwayi; in Brazil, braziliensis; and these differ in the 
amount of pigment in the feathers. By subjecting the birds of the 
northern type to an espécially moist atmosphere, Beebe caused them 
to be so influenced that with each new moulting, whether natural or 
artificially induced, they always developed darker feathers. Thus a 
wild bird having pigment in 25.9 per cent of its area, would have after 
the second moulting under experimental conditions, 38 per cent and 
after the third, 41.6 per cent. Thus during the experiment the 
typical form assumed the appearance of the three other forms and 
finally developed plumage markings which have never been seen in 
nature. Fig. 55 shows the type form, inca, the three geographical 
variants, and the darkest artificially produced form. 
