I40 PATTERNS AND PROBLEMS OF DEVELOPMENT 



gradient was observed with the nitroprusside reaction for gkitathione. 

 Although a basipetal reduction gradient appears in their material, their 

 conclusion is that there is no actual gradient but that the basal region 

 produces a substance inhibiting metabolism and raising redox potential; 

 this decreases in concentration acropetally and so gives the appearance 

 of a basipetal gradient. This substance and its effects are entirely hypo- 

 thetical, no evidence of its existence being given. They, of course, do not 

 accept the interpretations of the Runnstrom school or the conclusions of 

 Spek. 



OTHER DATA AND HYPOTHESES 



The indophenol blue reaction with extremely dilute reagents, which 

 permit appearance of intracellular indophenol blue in the living animals, 

 gives a very distinct basipetal color gradient in blastulae and gastrulae of 

 Asterias, supposedly indicating a gradient of active indophenol oxidase. 

 Unfortunately, attention was not given to the question of presence or 

 absence of a ventrodorsal gradient (Child, 1915a). Susceptibility of the 

 sand dollar Echinarachnius parma to a number of agents is like that of 

 Arbacia (J. W. MacArthur, 192 1), and dye-reduction gradients of another 

 sand dollar, Dendraster excentriciis , are like those of Strongylocentrotus but 

 more distinct (Child, 1936a). The question whether the change in condi- 

 tion indicated by dye reduction in Strongylocentrotus and Dendraster oc- 

 curs later in Arbacia and Echinarachnius remains open for further investi- 

 gation. 



In a long series of papers from 1914 on, Runnstrom has advanced a 

 hypothesis of gradient pattern of sea-urchin egg and embryo in terms of 

 two opposed overlapping gradients in the polar axis. These are regarded 

 as concentration gradients of specifically different substances, the "ani- 

 mal" gradient decreasing in concentration basipetally, the "vegetal" gra- 

 dient acropetally. Ventrodorsality is considered to be represented by an- 

 other concentration gradient approximately at right angles to the polar 

 gradients; and the lateral asymmetry of the larva, by still another. Since 

 these are regarded as coexisting and interpenetrating, each must differ 

 specifically from the others. His co-workers, particularly Horstadius and 

 Lindahl, have applied this hypothesis in interpretation of their experi- 

 ments on echinoderm development.^^ 



Using potassium-free sea water with several species of sea urchins, 

 Runnstrom (1925a) finds a differential susceptibihty to lack of potassium 



2' See Runnstrom, Horstadius, and Lindahl in Bibliography. 



