THE AXIAL GRADIENTS IN HYDROZOA. 2O3 



gradient is partially or wholly reversed by the irradiation of ex- 

 citation from the parent animal into the bud (p. 195). This pri- 

 mary gradient is then the same in all agents used. The late bud 

 stages show essentially the same relations as the full grown ani- 

 mals and are considered with the latter. 



Since the modifications of the primary gradient under consider- 

 ation appear most distinctly and under the widest range of con- 

 ditions in H. oligactis, they are first described as they occur in this 

 species, and this description serves as a basis for comparison with 

 the other species. 



Experimental conditions and results with alcohol and ether 

 are briefly as follows: the higher concentrations, ether 2-3 per 

 cent., alcohol 3-5 per cent., are added rapidly to well extended 

 animals in a little water and the dishes covered with exclusion of 

 air. The tentacles and hypostome region are usually completely 

 paralyzed in the extended condition before they are able to 

 contract at all, the body begins to contract and usually succeeds 

 in completing a strong contraction, but after that shows no fur- 

 ther movement, and the stalk, which under normal conditions 

 usually contracts later than the body, is either paralyzed before 

 it can contract, or transmission of the stimulus from the body and 

 excitation of the stalk are inhibited by the anesthetic before the 

 stalk reacts. Fig. 65 shows an animal with advanced bud in the 

 condition characteristic of this method of procedure. The ten- 

 tacles are completely paralyzed, the body has contracted strongly 

 and the stalk remains extended in both parent and bud. Under 

 these conditions the disintegration of tentacles and hypostome 

 is delayed as compared with that of the body, disintegration be- 

 ginning in a zone just below the tentacle bases and in the tips of 

 the tentacles at about the same time (Fig. 65). Disintegration 

 progresses basipetally in both tentacles and body and also through 

 the stalk (Fig. 66), the foot being the last region to disintegrate. 

 The stalk usually undergoes a very slow decrease in length 

 shortly before, or when disintegration begins (cf. Figs. 65 and 66). 

 This is perhaps a response of the muscular portions of the cells 

 to direct excitation by the reagent, or it may be an expression of 

 the elasticity of the mesoglcea or other tissues, appearing after 

 complete muscular paralysis. 



