THE AXIAL GRADIENTS IN HYDROZOA. 1 93 



the figures concern primarily the ectoderm it should be noted 

 that in well-fed animals the entoderm disintegrates at about the 

 same time as the ectoderm, or in many cases somewhat earlier. 

 Often disintegrated entoderm begins to flow out of the mouth 

 before disintegration of the body ectoderm begins, and in the 

 tentacles it can be directly observed that entodermal disintegra- 

 tion keeps pace with or follows very soon after disintegration of 

 the ectoderm. In starved animals, however, the entoderm is 

 distinctly less susceptible than the ectoderm, the difference be- 

 tween the two layers increasing up to a certain point with the 

 progress of starvation. This difference between starved and fed 

 animals is undoubtedly associated with the decrease in the meta- 

 bolic activity of the entoderm in the absence of food. In the 

 starving animal the functional activity of the entoderm must 

 undergo very considerable decrease, while the functional activity 

 of the ectoderm continues or may even increase with increasing 

 "hunger." 



The mesoglcea does not disintegrate, and the general form of 

 the animal is retained even after disintegration, except where 

 there is considerable movement of the fluid, but the replacement 

 of cellular structure by cellular detritus, and the increase in 

 transparency, except in the dyes, make it possible to distinguish 

 without difficulty the occurrence and progress of disintegration. 



THE PRIMARY GRADIENT IN BUDS. 



The earlier stages of buds before motor activity has developed 

 to any marked degree show the same susceptibility relations in 

 all three species and in all directly lethal concentrations of all 

 agents used. The earlier stages in which the bud is merely a 

 slight protuberance of the body wall, usually show no gradient 

 distinguishable from that of the region to which it is attached, 

 but sometimes even these early stages show the basipetal gradi- 

 ent characteristic of later stages (Figs. 14, 15). As the develop- 

 ment of the bud progresses, however, a distinct disintegration 

 gradient, basipetal with respect to the bud axis, makes its appear- 

 ance (Figs. 14, 15) and in early stages of tentacle-development, 

 but before the stalk has developed, the gradient is uniformly 

 basipetal in both tentacles and column (Figs. 16-19) an d under 



