264 PROBLEMS OF RELATIVE GROWTH 



where y = organ-size, % = body-size, and a, b, c, d are con- 

 stants. Most of these have no assignable biological signi- 

 ficance. 



If the measurements contained in the original papers were 

 re-analysed, it is probable that a number of cases of simple 

 heterogony would be revealed. I have done this for one or 

 two organs. E.g. testis weight (S. Hatai, 1913, Am. J. Anat., 

 15, 8y), after an early period of rather slow growth, where 

 more data are needed, shows a good approximation to simple 

 heterogony between body- weights 25 g. and 95 g., with growth- 

 coefficient about 1-65. After this, it enters on a phase of 

 negative heterogony, with k only about 0-4 to 0-45. The 

 ovary shows a very similar set of three phases, but the points 

 are more irregular. 



The hypophysis shows an interesting sex-difference. From 

 body-weights of 60 g. on, k for the male hypophysis is positive 

 (k about 1-3), whereas for the female it is negative (k rather 

 below o-8). Below this size, the points are rather irregular, 

 but those for both sexes appear to fall on a prolongation of 

 the curve for large females. 



For heart -weight (males) k is close to o-8 from body- weight 

 140 g. on. Before that, the points are more scattered, but 

 could be considered as fitting the same curve, though appar- 

 ently with a temporary acceleration of relative growth from 

 body- weight 60 to 120 g., later compensated for. 



The kidneys (males) begin by being somewhat negatively 

 heterogonic (k about 075), and then, after an irregular period, 

 show definite positive heterogony from body- weight 180 g. on, 

 with k close to i-i. Lung- weight (males) is more irregular, 

 but roughly approximates to a negative heterogony of growth- 

 coefficient about o-8 throughout. For further analyses along 

 these lines the data should be re-grouped into larger size- 

 classes. 



T. C. Byerley (1932, J. Exp. Biol., 9, 15) has recently shown 

 that in chick embryos allantois weight shows negative hetero- 

 gony relative to egg- weight, being roughly proportional to the 

 two-thirds power of egg- weight. It may be recalled that egg- 

 weight, at least in large birds, is itself roughly proportional 

 to the two-thirds power of body- weight (p. 226). 



He further points out an important connexion between rela- 

 tive and absolute growth. In fowls, gut-weight shows negative 

 heterogony (H. B. Latimer, 1924, /. Agr. Res., 29, 363). 

 Byerley finds a linear relation between feed-consumption and 



