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THE AMEBIC AN NATURALIST [Vol. L 



has been accomplished fundamentally by the same means 

 in all— a changed metabolism, in which a higher water- 

 content of germ and higher metabolism for male-produc- 

 tion, and lower water-content and decreased metabolism 

 for female production, have been definitely shown to be 

 associated in a number of instances. Whitman learned 

 in pigeon hybridization an additional— an entirely dif- 

 ferent— means of accomplishing the same end of height- 

 ening the metabolism of the germ. And, this additional 

 means definitely tends toward male-production. The 

 wider the cross (within the limits of the ' 1 developmental 

 compatibilities" of the germs) the greater the vigor and 

 strength added by the mere act of crossing— and at the 

 same time the more assuredly will such crosses produce 

 males. Even the closely related varieties used in most 

 Mendelian crosses have not failed to indicate the greater 

 vigor of the heterozygote. 



A sixth series of studies has been made on size of the 

 parents and offspring concerned in these sex-controlled 

 series. Seasonal and age fluctuations in the parents, and 

 in both sexes of both parent species ; size of offspring as 

 related to their sex, to season, and to the egg of clutch, 

 have been studied during three and one half years. We 

 have found no subject that presents so many complica- 

 . tions as does the matter of the size of offspring in this 

 series. Only a single aspect of the matter will be treated 

 here. The seasonal fluctuation in size of the parents used 

 in the 1 'overworked" or sex-controlled series is, how- 

 ever, a simple matter. Our results show— as indicated 

 by the lower curve on the chart (l)-that such parents 

 weigh most in winter and spring; least in the autumn, 

 reaching a minimum in August and September. In other 

 words, during the period when the female parent lays 

 her largest eggs, she herself, and her consort, are smallest 

 m size. I have had no charts prepared showing the sea- 

 sonal curves for individual birds, but data for such curves 

 m great number are available. 



Now, the single word I wish to say on the relation of 

 size m the offspring to the order of the eggs of the clutch, 



