446 ON INCREASE IN SIZE [pt. iii 



was only just keeping pace with the growth of the embryo. In these 

 circumstances, it was not surprising to find now an accumulation 

 and now a flushing out of waste products from the embryonic body. 

 In a later paper, however, he modified considerably his views on this 

 subject. 



As regards the growth of individual parts, Schmalhausen later 

 introduced several further expressions. "Homonomic growth", in 

 his terminology, means growth of an organism in which all the parts 

 and organs have the same growth-constant, "heteronomic growth" 

 — the more usual form — is the growth of an organism composed of 

 organs each with its own characteristic growth-constant. Then the 

 growth-directing force may exist either inside or outside the anlages of 

 the separate organs — in the chick it apparently does not exist inside — 

 and in the former case it would be called "autonomic growth", in 

 the latter " automorphic ", while, if the influence was directly the 

 growth of another organ, it would be termed "heteromorphic". 

 Schmalhausen found that, although the organs in the chick embryo 

 taken at any one moment had very different rates of growth, yet, 

 if they were all dated, as it were, from the time of formation of their 

 anlages, they showed very similar rates of growth. Thus an anlage 

 developing late would be growing much quicker than the whole body, 

 while, at the same time, if its instantaneous percentage growth-rate 

 curve was plotted, it would be found to have a shape very like that 

 of the organism as a whole. Thus organs can only be compared as to 

 their growth-rates if they are taken from their own particular origins 

 and not from the origin of the body as a whole. In homonomic growth, 

 of course, one is dealing with organs originating at the same time and 

 having identical growth-constants. In this case, the definite pro- 

 portions of the resulting organism can be deduced from those of the 

 anlages ; in other words, a kind of preformation holds good. 



If Table 56 be again referred to, it will be seen that, on the whole, 

 it takes functioning organs longer to grow than functionless ones. 

 Thus the metanephros, which at first has a Cvt of 359, drops to 196 

 after it has begun to excrete actively by about the i6th day. In 

 Fig. 58 is shown the relation between the weights of the organs in the 

 embryo chick expressed as percentages of the total weight of the 

 body. The heart and mesonephros are seen to have their maximal 

 relative size very early in development, after which the former 

 declines slowly and the latter more rapidly. The first four days of 



