THE COEFFICIENT OF GROWTH-PARTITION 51 



equilibrium be upset, regulation towards the equilibrium 

 position will occur during later growth. The particular 

 mechanism by which the equilibrium is attained does concern 

 growth-ratio ; the more the organ is below equilibrium-size, 

 the higher will be its growth-ratio. 1 (See Fig. 30.) 



These conclusions are supported by various lines of evidence. 

 In the first place, in cases of grafting of organs we should 

 expect the organ of a young animal grafted on to an older 

 and larger animal to be accelerated in its growth until it 

 reached a size prescribed by its growth-partition coefficient, 

 and the organ of an older animal grafted on to a younger 

 and smaller animal to be correspondingly retarded in its 

 growth. For the first, we may turn to the results of Wachs 

 (1914). When he inserted the lens of a young Urodele larva 

 into the eye of an older larva from which the lens had been 

 previously removed, the small lens was accelerated in its 

 growth. For the second, as well as the first, we have an 

 example in the work of Twitty (1930). Here cross-trans- 

 plantation was made between larvae of Ambly stoma tigrinum 

 and A. punctatum. The latter species grows much more slowly 

 than the former. Twitty removed the eye of a punctatum 

 larva and replaced it by one of the same size from a tigrinum 

 larva ; owing to the higher growth-rate of tigrinum, the age 

 of the donor was much less than that of the host. Even 

 when the host was fed only minimally, the grafted eye now 

 increased in size much more rapidly than that of the host : 

 in one case it increased 50 per cent, in diameter while the 

 host remained stationary in length. (See p. 197.) 



The converse experiment consisted in removing the eye 

 from a tigrinum larva and engrafting in its place an eye of the 

 same size from a considerably older punctatum larva. In this 

 case, the grafted eye made very slow growth. Here the rate 

 of growth could be compared with that made by punctatum 

 eyes grafted into A. tigrinum during the embryonic period. 



1 In some cases at least the change in growth-ratio will occur accord- 

 ing to the law enunciated for Sphodromantis by Przibram, 1917 : 

 When Z is the normal final length of the regenerating limb, n the 

 length after amputation, r its length at the beginning of a given period 

 of time t, R the length at the end of the time t, V a the normal 

 coefficient of increase of the limb between one moult and the next, 



then Z — n — y = — — ; and the growth-partition coefficient 



represents the limiting value of the growth-ratio when equilibrium is 

 established. 



