THE PHYSIOLOGY OF DEVELOPMENT 207 



the axial pattern is established and further development is 

 mainly concerned with increase in size. The existence of an 

 antero-posterior metabolic gradient in the earthworm is seen 

 from the following data : — 



Earthworm Experiments (Haldane's Methxod). 



Temperature 12-5° C. 760 mm. Hg. All values reduced to 5 c.c. 

 NH3 Kjeldahl. 



(i) In 3 hours worm consumed head 1*3 cub. mm. oxygen. 



tail 0-3 



(2) „ „ head 0-85 

 „ „ tail 0-27 



(3) „ ,, head o*75 

 „ ,, tail o'25 



In a second series of experiments Shearer investigated 

 the action of acetone powders instead of living tissues, the 

 former being prepared after the manner of acetone yeast 

 preparations by dehydrating the fresh tissue in acetone and 

 subsequently desiccating it. Such powders on being made 

 into a thin emulsion in distilled water take up oxygen. If the 

 powder prepared from the head region has a greater oxygen 

 capacity than powder prepared from the tail region, it is 

 impossible to escape the conclusion that the head region has 

 an intrinsic power to consume oxygen more rapidly, 

 independently of its structural organisation. This is indeed 

 the case. The results were again reduced to a fixed amount 

 of protein, i.e. in terms of 100 c.c. NH3 (Kjeldahl). The dura- 

 tion of each experiment was one hour twenty minutes at a 

 temperature of 40 C. and standard pressure. The oxygen 

 consumption in three experiments with acetone powders 

 from 6-7 embryos estimated by Barcroft's method is given 

 in cubic millimetres as follows : — 



(i) Head o'62 

 Tail o"23 



(2) Head 0*52 

 Tail 0*29 



(3) Head 0*47 

 Tail o"27 



The axial gradient hypothesis has naturally aroused con- 

 siderable hostility ; it is subversive of the underlying assump- 

 tions of the germ layer theor^^ For this reason the independent 



