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 



30 



35 '40 



m l 



45 



55 GO 65 70' 75 



tn 2 



90 95 



m 3 



FIG. 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 



FIG. 8. a, Typical wild pigeon, Scardafella inca; b', the form dialcucos; 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 m\ t ra 2 and m 3 

 respectively. 



