SECT. 2] 



AND WEIGHT 



435 



C JO 



J3 





a 10 



arguments of Brody. Schmalhausen speaks of the "wahre Wachs- 

 tumsgeschwindigkeit " instead of the instantaneous percentage 

 growth-rate, and of r instead of k. His equation relating the in- 

 stantaneous percentage growth-rate to the Minot growth-rate is 

 exactly the same as Brody's, and he points out that, when, according 

 to the old method, the growth-rate would be 700, the instantaneous 

 method would give a result of 207, though 50 per cent. (Minot) 

 would be equivalent to 40-5 (instantaneous). These figures might 

 have been read off from the 

 graph of relation given by 

 Brody, and it is surprising 

 that the two workers, one 

 at Kiev and the other in 

 Missouri, should have been 

 thinking on such very similar 

 lines. It is still more surprising 

 that embryologists had not 

 thought on such lines long 

 before. Schmalhausen and 

 Brody diverge, however, 

 upon one important point, 

 namely, the shape of the line 

 given when the log. weight is 

 plotted against the age, for 

 Schmalhausen regards it as a curve — just as Murray and McDowell 

 do — while, as we have seen, Brody lays great stress on the repre- 

 sentation of it by a series of straight lines having abrupt breaks between 

 them. Thus, the instantaneous percentage growth-rate, which with 

 Brody remains constant over certain definite periods, with Schmal- 

 hausen continually declines in value. In other words, Brody's diagram 

 which shows the instantaneous percentage growth-rate dropping 

 in a stepped formation from fertilisation to hatching is replaced in 

 Schmalhausen's work by a regular curve passing downwards to 

 become asymptotic to the abscissa (Fig. 55 h), just as the Minot curve 

 does, only, of course, plotted from a set of figures having a real 

 meaning as against the abstractions of Minot. This difference of out- 

 look leads naturally to very wide differences in conclusions; thus 

 Schmalhausen has nothing to say about critical points or hidden 

 metamorphoses. Having diverged from Brody in this direction, 



28-2 



10 n n 16 



20 Zl 



Age in days 



P=wet weight; 

 Cv = instantaneous % growth-rate. 



Fig. 55 *• 



