588 ON INCREASE IN COMPLEXITY [pt. iii 



electric potential, even in the case of invertebrates — tubularians, 

 planarians, annelids, etc. Are we then justified in asserting, direct 

 evidence being absent, that a similar relation holds for vertebrates 

 and embryos in general? Hyman's few figures for respiration of 

 Fundulus eggs tell us nothing about the metabolic rate, for no weighings 

 of embryos were made. As regards the embryo, it is most unfortunate 

 that the only other piece of relevant evidence is contradictory. 

 Shearer in 1923 made an investigation of the oxygen consumption 

 of the head end and the tail end of chick embryos, using the Barcroft 

 differential manometer. Fig. 96, taken from his paper, shows the 

 results which he obtained. On the 4th day the head pieces took up 

 more than three times as much oxygen per gram per hour as the 

 tail pieces did, but by the loth day the two curves had almost come 

 to coincide. Both of them fell, showing that the metabolic rate of 

 the cells was declining with time in the usual way. Such a graph 

 fits in very well with the morphological picture, for by the loth 

 day the axiate pattern has long been established, and subsequent 

 development mainly concerns growth in size. Shearer went on to 

 investigate the action of acetone powders in order to see whether 

 the higher metaboHc rate of the head pieces was dependent on 

 structural conditions. The powders were made in the same way as 

 acetone yeast preparations by first dehydrating the tissue in acetone, 

 and subsequently desiccating completely. Such powders on being 

 made into a thin emulsion with distilled water respire. The results 

 were as follows: 



c.c. oxygen taken up by embryos of 6-7 days' development per amount of 

 tissue containing 1-4 mgm. nitrogen. 



Exp. Head Tail 



1 0-62 0-23 



2 0-52 0-29 



3 0-47 0-27 



•This then aflforded a clear demonstration in favour of the identifica- 

 tion of metabolic rate gradients with axial gradients, and gave 

 evident support to Child's views. Unfortunately, in a later state- 

 ment Shearer reported that he had not been able to repeat these 

 findings, and that further experiments had very much modified the 

 original conclusions. "I have since concluded", says Shearer in a 

 private communication, "that I was dealing with the rate of cytolysis 



