196 



PROBLEMS OF RELATIVE GROWTH 



16 ~Q) T whole eye on P 



T whole eye on P Qy~ 



15 



14 



13 



1-2 



-(g) T optic vesicle onP 

 -(3) T lens ectoderm on P 



II ■ 



T lens ectoderm onP($y 



T optic vesicle on P (9)- 



association, of a slow-growing optic vesicle with a fast-growing 

 lens, accelerates the growth of the optic vesicle in a tigrinum 

 body by 25 per cent. (No. 5), and by 22 per cent, in a punc- 

 tatum body (No. 3). And it retards the growth of the lens 

 by 20 per cent, in a punctatum body (No. 9), by 21 per cent, 

 in a tigrinum body (No. 10). The regulation is a gradual one, 

 as shown by Harrison's Fig. 37. 



Further, Harrison gives conclusive proofs that the regula- 

 tion is due to chem- 

 ical and not in any 

 appreciable degree 

 to merely mechani- 

 cal causes. He also 

 finds some regula- 

 tion of a similar sort 

 in other tissues in 

 the proximity of the 

 eyes. 



We could inter- 

 pret these results in 

 various ways. Per- 

 haps both rapid- 

 growing and slow- 

 growing organs pro- 

 duce specific sub- 

 stances which in- 

 teract with each 

 other. Perhaps 

 there is only one 

 type of substance, a 

 positive or growth- 

 promoting sub- 

 stance ; in such 

 case, when there is 

 a deficiency of this 

 in, e.g., the slow-growing lens, there will be a greater differ- 

 ence in concentration of this substance between optic vesicle 

 and lens, therefore more diffusion of the substance left in the 

 optic vesicle and accordingly less rapid growth of the opt c 

 vesicle. This latter suggestion would be in harmony not only 

 with the facts as to growth-centres and growth-gradients here 

 set forth, but also with recent work on plant growth, e.g. by 

 Dolk, who finds a specific growth-hormone with quantitative 



10 



9 



8 



7 



6 



@P lens ectoderm on T 

 (§)P optic vesicle on T 



-(6) P whole eye on T 



P opt/c vesicle on T (jdy^ 



P lens ectoderm on T(Th 

 P whole eye on T Qz) 



(a) 



(b) 



Fig. 87. — Diagram to show the results of grafting 



whole eyes and their parts between Ambly stoma 



tigrinum (T) and punctatum (P). 



The ordinates give the ratios of the linear dimensions of (a) the 

 optic bulb and (fc) the lens on the side receiving the graft to those 

 of the intact eye of the other side (see text for details). 



(Constructed from Table II in Harrison, 1929B.) 



