422 



THE PREFUNCTIONAL AS CONTRASTED WITH 



organs (such as crustacean chelae), within single regions of the 

 body (such as in the crustacean abdomen), or within the body as 

 a whole (as in stag-beetles or Planarians).^ The third is concerned 



16 

 15 

 /4 

 13 

 12 

 II 

 JO 

 0-9 

 8 

 07 

 6 



r-Q) T wh<jk eye on P 



-<2) T optic vesicle onP 

 -(D T lens ectoderm on P 



g)P lens ectocLerm on T 

 [5) P optic vesicle on T 



-@P whole eye on T 



T whole eye on P 0- 



Tlens ectoderm onP@^ 

 T optic vesicle on P (9)- 



P optic vesicle on T(id)^ 



P lens ectoderm on T(Th 

 P whole eye onT {0 



(a) 



Fig. 204 

 The mutual influence of regions with diflferent specific growth-intensities. 

 Whole eyes, or their parts (optic vesicle and lens ectoderm), were grafted reci- 

 procally between embryos of Amblystotna tigrinum (T) with high growth- 

 intensities, and Ajnbly stoma pwictatum (P) with low growth-intensities. The 

 ordinates represent the ratios of the diameters of the parts of the eye on the side 

 receiving the graft to the diameters of the corresponding parts of the intact eye 

 of the other side, (a) for optic vesicle, (b) for lens. Fast-growing whole eye on 

 slow-growing host (i and 7) gives high ratios. The association of a slow-growing 

 host-lens with fast-growing grafted optic vesicle (2 and 9), or a slow-growing 

 host optic vesicle with grafted fast-growing lens (3 and 8) reduces the ratios. 

 Similarly, low ratios are found for slow-growing whole eyes on fast-growing 

 hosts (6 and 12); 5 and 10, 4 and 11 show the increase of ratio when a slow- 

 growing grafted component is associated with a fast-growing host component. 

 (From Huxley, Problems of Relative Growth, London, 1932; based on data of 

 Harrison.) 



with the time-relations of development. In general, development 

 occurs in an antero-posterior direction, so that at a given time an- 

 terior organs are further differentiated than those at a more posterior 

 ^ See Huxley, 1932, Chap. in. 



