24 GENETICS IN RELATION TO AGRICULTURE 
in head and shell length as found on successive dates from June 3 to 
January 3. By raising these animals under constant temperature condi- 
tions and varying the strength of the nutrient solution, Woltereck proved 
Fic. 7.—Schematic curves of head-height in Hyalodaphnia as grown in media of three 
different food values. (After Woltereck from Goldschmidt.) 
that the relative size of body parts varied with the food. In Fig. 7 the 
percentages of head height to shell length are plotted as abscissas and 
the numbers of individuals as ordinates. Animals from three strengths 
a b c d e 
Fia. 8.—a, Typical wild pigeon, Scardafella inca; b, the form dialeucos; c, braziliensis; 
d, ridgwayi; e, S. inca after three moultings in a moist atmosphere. (After Beebe from 
Goldschmidt.) : 
of nutrient media were measured, the curves of those from the weaker, 
the medium and the richer media being shown at mj, mz and m3 
respectively. 
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