THE AXIAL GRADIENTS IN HYDROZOA. 83 



tentacles, never, so far as my observations go, at the same time, 

 and progresses basipetally on the manubrium, the basal portions 

 of the hydranth body being the last to show color. The color 

 appears first on the external surface and it is not infrequently 

 possible to see the formation of precipitate on the external surface 

 of the cells. Such precipitate must result from reduction of 

 permanganate on the external surface of the protoplasm and the 

 reduction and coloration progress from the surface inward. The 

 permanganate does not penetrate the living cell and kill after it 

 attains a certain concentration in the interior but it reacts with 

 the protoplasm and undoubtedly kills it as it comes into contact 

 with it. 



The color deepens rapidly and within fifteen minutes to an 

 hour in concentrations ranging from m/2ooo to 772/7500 the regions 

 where coloration first appeared are deep brown or opaque black 

 and from these a color gradation to yellow in the basal regions 

 appears. 



After two to three hours the whole hydranth is usually opaque 

 black in water. Teasing shows that at this time reduction has 

 occurred throughout the ectoderm and that the entoderm is more 

 or less deeply colored, and sometimes gradual differences in rate 

 of entodermal staining can be seen, but the existence of ento- 

 dermal gradients can be determined with certainty only in 

 dehydrated and cleared material. After reduction is completed 

 all hydranths are opaque black in transmitted light, and even 

 after dehydration and clearing the bodies of the larger hydranths 

 are opaque throughout, but the gradient is distinct in all tentacles 

 and in at least the smaller hydranths. 



The diagrammatic Fig. I indicates the color gradients in the 

 tubularian Bougainmllea. The lighter side of the figure shows 

 the gradient in rate of staining in single tentacle and the hydranth 

 body, as seen from the surface after fifteen minutes to one hour 

 in KMnO 4 according to concentration. The right side of the 

 figure represents an optical section of tentacle and body wall 

 after complete reduction, dehydration and clearing. The shading 

 is intended to give some idea of the differences in depth of staining 

 at different levels. After total reduction and clearing all parts 



