EMBRYONIC GROWTH 141 



line of argument. We wish to find the growth-quotient q of 

 an organ — i.e. the ratio of the growth-rate of the organ during 

 a particular phase of its development to that of the body, 

 or of a standard part representing the body, not during the 

 same period of time, but during the corresponding phase of 

 its development. 



Schmalhausen had previously established the following 

 formula for finding what he calls the true growth-rate (C„) of 

 an organ for a period from time t to time t u during which 

 the weight (or volume) of the organ has increased from v 

 to v x . His formula is 



_ log^ x -log v .. 



U ~ 0-4343 Ci-*) W 



Correspondingly the true growth-rate of the body during 

 the same period will be 



log ^-log* (la) 



0-4343 (h-t) K ' 



If organ and body are in the same phase of development 

 during this period, then the growth-quotient q is 



Q, = logtti -logy . . . . ( a ) 



This is simply another method of writing the heterogony 

 formula already arrived at by me, and his q is the same as 

 my k. 



For purposes of dealing with embryonic organs, we should 

 take t as t , the time at which the organ and the body begin 

 their growth, which in this case we have assumed to be at the 

 same moment. We should then write v and w, v and w 

 respectively. Formula (2) can then be written : 



Log v t = q log w 1 + (log v — q log w ) • . (3) 



Now log Vo — q log Wo will always be the same ; let us call 

 this expression b. 



Then v x = bw^. 



As stated above, q is here identical with k in my formula ; 

 but we now have a further analysis of my constant b, which 

 however can only be arrived at if we know the initial size of 

 the organ and the body-standard. 



But if the organ and the body begin their growth at different 

 times, then the matter is more complex. We want to com- 

 pare the growth of the organ with that of the body during 

 corresponding periods of their development. Let t x be the 



