THE AXIAL GRADIENTS IN HYDROZOA. 



C. M. CHILD, 

 FROM THE HULL ZOOLOGICAL LABORATORY, THE UNIVERSITY OF CHICAGO. 



IV. AXIAL GRADATIONS IN RATE AND AMOUNT OF REDUCTION 

 OF POTASSIUM PERMANGANATE IN VARIOUS HYDROIDS 



AND MEDUSAE. 



In an earlier paper (Child, '190) attention was called to a 

 method of rendering directly visible the physiological axial 

 gradients in many of the simpler organisms and earlier develop- 

 mental stages through the differences in rate and in total amount 

 of reduction of potassium permanganate by the protoplasm of 

 different regions and levels. Since the reduced permanganate 

 (MnO 2 or other oxides) colors protoplasm brown to opaque 

 black according to amount of deposit, differences in rate or 

 amount of reduction in different regions appear as differences in 

 depth of coloration or in degree of opacity. 



In the paper referred to, the results of work with permanganate 

 on various animal and plant species are briefly described and it 

 is pointed out that the gradients in rate and amount of per- 

 manganate reduction correspond to the physiological gradients 

 demonstrated by means of the susceptibility method and various 

 other methods. 



MATERIAL AND METHOD. 



The present paper records observations made on the reduction 

 gradients, as they may for convenience be called, of various 

 species of hydroids and medusae. The work was done at the 

 Puget Sound Biological Station chiefly during the summers of 

 1918 and 1919 and I am indebted to the director for the privileges 

 of the station. The data concerning the hydroids were obtained 

 chiefly from four species, Bougaiwuillea mertensi, Gonothyraa 

 darki, Obelia borealis and 0. longissima: but observations on 

 rate of reduction were also made on several other campanularian 

 species. Young hydroids were grown in the laboratory from the 

 eggs of Gonothyrcea and the hydromedusa Phialidium gregarium 



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