154 FAMILY STUDIES IN BUILD. 



20. By comparing coefficients of variability instead of indices, and 

 by making allowance for the greater range of the fleshy class than the 

 slender class, it still appears that the progeny of fleshy parents are 

 relatively and per unit range more variable than the progeny of 

 slender parents. Absolutely the offspring of the fleshy parents are, 

 as stated, twice as variable as of slender parents. 



21. The matings of slender parents and fleshy parents of fleshy 

 stock yield a variable progeny, such as is typically found in the Fi 

 generation when multiple factors are concerned. The variability is 

 between that of the progeny of slender matings and that of the 

 progeny of fleshy matings. 



22. The Fi generation has not a mode of build that is intermediate 

 between that of the parental stocks, but one that is about the same 

 as of the fleshy matings. This is evidence of partial dominance of 

 fleshiness. 



23. The mating of two heterozygous (Fi) parents produces, in gen- 

 eral, an exceptionally variable progeny. This is one of the strongest 

 evidences of the presence of genetical factors in build. 



24. Many, if not most, parents of medium build belong to biotypes 

 with 1 or 2 independent factors for build. Consequently the progeny 

 of medium X medium matings is often strikingly invariable. 



25. The "back-cross" of a heterozygous parent with a slender par- 

 ent, on the one hand, or with a fleshy parent of fleshy stock, on the 

 other, gives a variable progeny, whose mode is shifted toward fleshi- 

 ness; but which shows a tendency to fall again into the slender (or 

 fleshy) and medium-fleshy grandparental types. 



26. Variations in build are not to be accounted for merely by varia- 

 tions in intake and out-go of calories, but also by the endogenous 

 factors that determine the "economy of nutrition" or the cost in 

 energy of adding an additional kilogram of weight to the body. The 

 factors involved in producing differences in these respects are 

 hereditary factors. 



27. The hereditary factors probably work through the intermediacy 

 of special organs that influence metabolism, notably the endocrine 

 glands. The latter thus intermediate between the chromosomal con- 

 stitution, on the one hand, and control of metabolic processes, on the 

 other. 



28. The number of factors involved in very fleshy build is, in some 

 cases at least, three independent ones. But the number is probably 

 not the same in all biotypes. Probably in some there is only one, 

 in others four or more. 



29. The factors probably influence the functioning of the thyroid, 

 pituitary, and perhaps other glands. 



