ANTERO-POSTERIOR DEVELOPMENT 135 



facts obtained by Przibram (1917) for the growth of limbs 

 in Sphodromantis are also a consequence of the law of antero- 

 posterior development. His Table B gives the growth-quotients 

 for the middle and hind limbs at each instar — i.e. the ratio 

 of the length at one instar to the length at the instar pre- 

 ceding. If these are averaged for groups of three moult-stages, 

 we obtain the following result : 



Growth-quotients 

 Moults Mid-leg Hind-leg 



2-5 . . . . . .1-211 I-2o6 



5-8 ...... I-26o 1-266 



8-11 ...... 1-293 1-297 



i.e. not only is there a steady increase in the growth-quotient 

 during life, but the growth-quotient for the mid-leg begins 

 higher but ends lower than that for the hind-leg. There are, 

 however, considerable irregularities in the values for single 

 instars, and it is possible that this result is not significant. 



That the law of antero-posterior development depends upon 

 some fundamental gradient within the body as a whole is 

 indicated by the work of Ruud (1929) who found that the 

 growth of a urodele leg-bud rudiment transplanted to the 

 arm-region was markedly accelerated, that of an arm -bud 

 rudiment transplanted to the leg region retarded. 



Regeneration as well as growth may be affected by this law. 

 For instance, Von Ubisch (1923) finds that if three equal 

 V-shaped pieces are cut out of the dorsal fin of Urodele larvae, 

 the regeneration of the anterior piece is almost always less 

 than that of the posterior. This latter result he ascribes to 

 the capacity for regeneration being inversely proportional to 

 tissue-differentiation, and to differentiation proceeding in an 

 antero-posterior direction. 



In Cloe, the capacity for regeneration remains unimpaired 

 throughout life, independently of differentiation which is com- 

 plete in all three limbs, so that we presumably obtain a direct 

 effect of the main axial gradient of the body upon rate of 

 regeneration. 



However, that the law of antero-posterior development, as 

 regards growth-effects, need not hold even in mammals is 

 shown by the measurements of whales given by Mackintosh 

 and Wheeler (1929 : see especially pp. 277-95). In these 

 animals the head is, of course, enlarged to carry out the highly 

 specialized straining function of the baleen on the jaws : and 

 accordingly we find that its percentage length relative to total 



