1^2 C. M. CHILD. 



isms and because the data of observation and experiment indi- 

 cate that differences in the rate of metabolism and particularly 

 of oxidation are characteristic features of these gradients. Pro- 

 toplasm is a system in which the chemical reactions of metabolism 

 are so intimately associated with other factors, e.g., colloid dis- 

 persion, active mass of enzymes, permeability of limiting sur- 

 faces, electrolyte and water content, etc., that to attempt to dis- 

 tinguish one particular factor rather than another as primary is 

 at present impossible. The axial gradients are not simply oxi- 

 dative or metabolic gradients but gradients in general physiolog- 

 ical state of the particular protoplasm concerned, and in this 

 physiological state oxidation and associated with it other meta- 

 bolic reactions are important factors. The term " metabolic 

 gradient " as used in this connection means only that the meta- 

 bolic factor is a characteristic feature of the gradients. The 

 term " physiological gradient " which avoids all specific implica- 

 tions might be substituted for it. 



In the development and differentiation of the axiate pattern 

 the apical region or head of the organism arises from the region 

 of greatest acitivity or highest metabolic or oxidative rate the 

 "high end" of the major or polar gradient and other organs 

 at different levels of the gradient. The simplest forms of radial 

 symmetry in which there is no differentiation between different 

 radii are in reality nothing more than an apico-basal pattern and 

 only an apico-basal gradient is present. In the more complex 

 forms of radial symmetry a number of radial axes or gradients 

 arise and the radially arranged parts differentiate in relation to 

 these. In bilateral patterns there is not only a gradient along the 

 longitudinal or polar axis, but bilateral gradients are also pres- 

 ent. In most bilateral invertebrates the high region of these 

 bilateral gradients is apparently represented by the median ven- 

 tral region and in the vertebrates by the median dorsal region. 

 The evidence indicates that the chief axial gradients appear 

 primarily in the superficial regions of the cell or multicellular 

 body and in many of the simpler organisms, e.g., many protozoa 

 (Child, 5 i4&) and plant cells they are throughout life present 

 only or chiefly in the superficial regions, but where definite local- 

 ized internal organs with an axiate pattern exist, these also show 



