PAPERS ON ZOOLOGY 291 



basis may be explained vrhy the females continue to in- 

 crease in size long after maturity is attained "while fully 

 mature males of any given species differ but little in size. 

 While the foregoing attempts to exi:)lain the physiologi- 

 cal basis for differences in relative development of the 

 body or of restricted regions of the body in the two 

 sexes, no hypothesis can be advanced to explain why 

 the modification of physiological processes regulating 

 growth becomes expressed in such widely varying man- 

 ners. It is not clear why stimulation to farther growth 

 should in one instance involve the entire body uniformly, 

 in another be confined chieflly to length, and at still other 

 times cause excessive enlargement of restricted areas 

 or of individual structures. 



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Child, C. M. 



1915. Senescence and Rejuvenescence. Univ. Chicago Press. 

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1900. Sexual dimorphism in the animal kingdom: a theory of the 

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 Darwin. C. 



1909. The descent of man and selection in relation to sex. Second 

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 Luhe, M. 



1911. Die Siisswasserfauna Deutschlands. Heft 16, Acanthocepha- 

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 MitcheU, P. C. 



1911. Sexual Dimorphism. Encyclopaedia Britannica, Eleventh 

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1915. Acanthocephala of North American Birds. Trans. Amer. 



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