206 THE RATE OF GROWTH [ch. 



hardly a measurable, change of form*; but the shapes and looks 

 of man and woman go on changing long after the growing age is 

 over, even all their lives long. A centipede has its many pairs of 

 legs alike, to all intents and purposes; they begin alike and grow 

 uniformly. But a lobster has his great claws a,nd his small, his 

 lesser legs, his swimmerets and the broad flaps of his tail ; all these 

 begin ahke, and diverse rates of growth make up the difference 

 between them. Moreover, we may sometimes watch a single Umb 

 growing to an unusual size, perhaps in one sex and not in the other, 

 perhaps on one side and not on the other side of the body: such 

 are the "horns," or mandibles, of the stag-beetle, only conspicuous 

 in the male, and the great unsymmetrical claws of the lobster, or 

 of that extreme case the httle fiddler-crab {Uca pugnax). For such 

 well-marked cases of differential growth-ratio between one part and 

 another, JuHan Huxley has introduced the term heterogonyf. 



Of the fiddler-crabs some four hundred males were weighed, in 

 twenty-five graded samples all nearly of a size, and the weights 

 of the great claw and of the rest of the body recorded separately. 

 To begin with the great claw was about 8 per cent., and at the end 

 about 38 per cent., of the total weight of the unmutilated body. 

 In the female the claw weighs about 8 per cent, of the whole from 

 beginning to end; and this contrast marks the disproportionate, 

 or heterogonic, rate of growth in the male. We know nothing 

 about the actual rate of growth of either body or claw, we cannot 

 plot either against time; but we know the relative proportions, or 

 relative rates of growth of the two parts of the animal, and this is 

 all that matters meanwhile. In Fig. 54, we have set off the successive 

 weights of the body as abscissae, up to 700 mgm., or about one-third 

 of its weight in the adult animal; and the ordinates represent the 

 corresponding weights of the claw. We see that the ratio between 

 the two magnitudes follows a curve, apparently an exponential 

 curve; it does in fact (as Huxley has shewn) follow a compound 



* Cf, S. Hecht, Form and growth in fishes, Journ. Morphology, xxvii, pp. 379- 

 400, 1916; F. S. and D. W. Haramett, Proportional length-growth of garfish 

 (Lepidosteus), Growth, in, pp. 197-209, 1939. 



t See Problems of Relative Growth, 1932, and many papers quoted therein. 

 The term, as Huxley, tells us, had been used by Pezard; but it Jiad been used, in 

 another sense, by Rolleston long before to mean an alternation of generations, 

 or production of offspring dissimilar to the parent. 



