SECT. 2] 



AND WEIGHT 



439 



them that organs which reach a high state of differentiation early 

 grow the most slowly (brain and lens), while less differentiated 

 organs grow most quickly (liver and limb-buds). The growth of the 

 body as a whole is the average practically exactly of the rest, and it 

 is interesting to note that the organ which most nearly approaches 

 it is the heart. The heart would seem to grow in size at the same rate 

 as the entire body. But, as Schmalhausen says, this growth in size 

 seems to have no simple relation to the growth in weight as shown 

 by the percentage growth-rate. 



Table 58. SchmalhauserC s values for a, i.e. daily increment in 

 size or '^ Lineargrdsse^\ 



Chick 



Duck 

 Man 



)> 

 Rat 

 Rabbit 

 Pig 

 Guinea-pig 



Whole embryo (ist half) 



(2nd half) 

 Brain 

 Lens 

 Spleen 

 Heart 

 Lung 

 Liver 

 Testis 



Metanephros 

 Stomach 

 Fore limb 

 Hind limb 

 Pectoral muscles 

 Whole embryo 



In a later paper Schmalhausen studied the relation between initial 

 weight and end weight in a number of animals, wishing to obtain 

 some means of comparing their " Wachstumsertrage " or Growth- 

 yields, on a basis independent of their size. He found that u, or the 

 mass of substance added on to itself by the organism between times 

 ti and tz, could be calculated by the formula 



u = 



t h *^i 0-4343 



