194 



PROBLEMS OF RELATIVE GROWTH 



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DAYS AFTER OPERATION 

 Fig. 86. — Similarity of relative growth of eye of two species of Amblystoma 

 with different absolute growth-rates. 



The curves are derived from the means from 5 specimens of each species, which were used in eye- 

 grafting experiments. They represent the ratio between the diameter of the normal unoperated eye 

 and the total length. 



The ratios decrease (negative heterogony) but are closely similar for the two species in spite of 

 the fact that during the period the mean-length of the tigrinum larvae had increased from about 

 14 to no mm., while that of the punctatum larve had only increased from about 13 to nearly 55 mm . 

 The operation was carried out in the embryonic period. 



they could eat. 1 By reversing the nutritive situation, the 

 amount of growth made by the grafted limbs could be reduced 



1 The matter is actually not quite as simple as this. From the 

 detailed results of Twitty and Schwind (1931) it appears that the 

 correspondence between grafted and control limbs only remains perfect, 

 even in maximally fed specimens, up to a certain time in larval life. 

 After this, there is a slight decrease in the size of the large limbs grafted 

 on to the small host, and a more considerable increase of the small 

 limbs grafted on to the large host (Fig. 85) — an effect the reverse of 

 that first posited by Harrison. It would thus appear that the size 

 of the host gradually comes to influence the inherent growth-capacity of 

 the graft, although this influence is always slight compared to the differ- 

 ence in the inherent growth-capacity of the organs of the two species. 



Further, Detwiler (1930) and Severinghaus (1930) claim that the 

 host may in some cases exert some effect upon the inherent growth- 

 rate of the graft in early stages before feeding begins. But what- 

 ever the extent of these minor effects, the specific growth-rate of the 

 organ is the main factor in determining its relative growth-rate when 

 transplanted. 



