DEMONSTRATION OF AXIAL GRADIENTS. 143 



These miscellaneous data on widely separated groups include 

 the chief results obtained thus far with permanganate. It 

 should perhaps be stated that in every case, except certain 

 hydroids, the siphonophore and actinians at least ten individuals, 

 and in the case of eggs and embryos hundreds or thousands were 

 used, and the experiments were repeated at different times. 

 With some of the hydroids only five or six branching stems from 

 different colonies were used with the same results in all cases. 

 In the case of the siphonophore three colonies were used, and 

 since the results fully confirmed those obtained by other methods, 

 and in each colony the same result could be observed in the 

 different groups of zooids, larger numbers were considered un- 

 necessary. Of the actinians three to six individuals of each 

 form tested were used, the uniformity of result in all the species 

 making large numbers unnecessary. 



DISCUSSION. 



The data briefly recorded above are sufficient to show that 

 axial gradients in rapidity of staining with MnO 2 produced by the 

 reduction of permanganate in low concentrations are at least of 

 very wide occurrence in axiate organisms and organs. Moreover, 

 in every case where data have already been obtained by other 

 methods these have been confirmed by the color gradient, and 

 in some cases slight symmetry gradients which were not visible 

 or were indistinct with other methods have been clearly seen. 



For various forms, including protozoa, medusa planulae, 

 echinoderm eggs and embryos and ascidian tadpoles, it has been 

 demonstrated that the color gradient appears only when the 

 living animals are brought into permanganate. When they are 

 first killed without disintegration by some other agent, e. g., 

 mercuric chloride, alcohol, etc., and then brought into perman- 

 ganate, staining is uniform, except where structural differences 

 are concerned, and the gradient does not appear. Like the sus- 

 ceptibility gradients, the color gradients are thus features of 

 living axiate organisms. This is undoubtedly true for all forms, 

 but its truth has not been proved for all. 



Only one further point need be considered here, viz., the ques- 

 tion whether the color gradients are merely a result of differences 



