396 SELIG HECHT 



vertebrates is very meagre, most of the work on growth having 

 been concerned with the weights of the body and internal organs.* 

 Sufficient data, however, exist to show that the rates of growth 

 of the parts of the body of higher vertebrates are different for 

 the different parts. 



Topinard ('85, p. 1030) gives the measurements of the length of 

 the head, trunk, thigh, leg, arm, and hand, in man from birth 

 to twenty years. I have calculated from the values given, the 

 rates of growth of these parts, and find that the parts have 

 rates of growth differing widely from one another. Thus during 

 the same period of time the head grows 55.8 per cent of its 

 former length, the trunk 59.8 per cent, the thigh 78.7 per cent, 

 the leg 69.5 per cent, the arm 60.6 per cent and the hand 52.3 

 per cent. Less complete measurements made by Menard ('85) 

 on the horse indicate the same lack of conformity in rate of 

 growth of the different parts. 



In man not only are there differences between the parts of the 

 body, but these difTerences do not remain constant. For, at 

 different periods in the growth of the individual the value of the 

 ratio between any given part and the total length varies con- 

 siderably. This condition is in strong contrast to the constant 

 and uniform relation found for fish, for the frog, and for Dosinia. 



Thus it seems possible to group on the one hand fishes and 

 probably frogs and Dosinia, in which growth is uniform but 

 unlimited (indeterminate), and on the other hand man and other 

 higher vertebrates, in which growth varies, finally ceasing alto- 

 gether (determinate). In animals with indeterminate growth 

 the form of the individual is laid down very early in life, and is 

 adhered to, within narrow limits, throughout its period of growth 

 — which means for the rest of its life. In higher vertebrates, 

 however, the form is continually changing during the period of 

 growth, and as soon as it becomes constant (the adult stage) 

 growth ceases." 



^ For a summary and critical discussion of such growth curves, see Meyer. 

 For a theoretical interpretation of them, see Hatai ('11). 



^ The nice point as to whether growth ceases because the form becomes con- 

 stant, or whether the form becomes constant because growth ceases, I shall not 

 attempt to discuss. 



