SIZE INHERITANCE IN DUCKS 135 



892 grams respectively. The difficulty of obtaining pure wild 

 mallards in parts of Europe is well brought out by Rogeron in his 

 work ''Les canards." 



Goldschmidt lays stress on the importance of environmental 

 factors in the growth rate of ducks. To show the influence of 

 earliness or lateness of hatch on body weight, I have prepared 

 table 3. In this table each of the four groups of 1912 ducks 

 (both sexes and both generations) were split into early and late 

 hatches, and the average age and average adult weight found for 

 each of the eight groups thus obtained. The result is very strik- 

 ing, and shows the advantage of lateness over earliness in every 

 one of the four cases. 



The growth curves show the same phenomenon. For example 

 in chart 4, curve F29I represents the weights of early hatched 

 birds and shows the greatest weight at 60 days of age but a very 

 low maturity weight at 105 days. On the other hand, curve 

 F295 (late hatched birds) shows a smaller weight at 60 days of 

 age but much greater weight at maturity. 



The early hatched birds tend to mature quicker and remain 

 smaller. This result only emphasizes the importance of outside 

 conditions as pointed out by Goldschmidt. 



In charts 2 to 5 growth curves are given for both sexes and both 

 generations of the cross-bred birds. Each curve represents the 

 average growth of one sex of each clutch of eggs. At the point 

 marked P, at 50 to 70 days of age, there is always a depression 

 which corresponds with the removal of the ducklings 'from the 

 rearing yard to the maturing yard, where the free access to water 

 and greater space tended for a short time to keep their weight 

 down. 



There is a slight tendency to a depression at the time of moult 

 from the first juvenile to the first adult plumage, which takes 

 place between the ages of 110 and 140 days. In all cases the 

 birds were in full plumage when killed, and the completion of the 

 full plumage is a very good criterion of the time when the adult 

 or autumn weight has been attained. Increase in weight beyond 

 this point seems to be due mostly to an increase of fat, and is 

 generally much more marked among the females than among the 



