1 1.. C. M. CHILD. 



is indicate that real physiological differences exist in the dif- 

 ferent bud stages. Probably the lower susceptibility of the 

 earliest as compared with later stages means that they have not 

 yet attained their maximum physiological activity as regions 

 of growth. The period of early bud development is certainly 

 a period of acceleration in physiological activity and so of in- 

 creasing susceptibility like the earlier stages of embryonic 

 development (Child, '150. Chap. XV.). Later, as differentia- 

 tion of the hydranth progresses, susceptibility again decreases. 



The sensitiveness of these hydroids to laboratory conditions, 

 as well as the close relation between susceptibility and physiologi- 

 cal condition is indicated by the fact that colonies kept over 

 night in standing water or even in aquaria with running water 

 very frequently show, either little or no difference or a more or 

 less complete reversal as regards the susceptibility of different 

 stages of development to KNC, i.e., those stages which were 

 originally most susceptible are either no more susceptible or 

 even less susceptible than other stages. A similar reversal 

 appears when the animals are stained for several hours in neutral 

 red and then killed in KXC. Reversals have also been observed 

 in various algae under the same conditions (Child, '166, '17). 

 In the hydroids, as in the alga 1 , it is evident that laboratory 

 conditions or neutral red alter the physiological condition of the 

 earlier, originally more susceptible developmental stages to a 

 greater degree than that of the later stages, and that this altera- 

 tion decreases the susceptibility of the earlier stages to KXC 

 to such an extent that it is equal to or less than that of later 

 stages. Since susceptibility to KXC shows a close relation to 

 rate of oxidation, it is probable that laboratory conditions and 

 neutral red decrease oxidation in some way and to a greater 

 degree in earlier than in later stages. In other words, this effect 

 ot laboratory conditions is itself dependent upon the differences 

 in susceptibility which exist in these organisms. Moreover, 

 this effect and that of neutral ml on the one hand, and that of 

 KXC on the other are evidently not additive, as the effect of 



S T C and lack of oxygen appear to be (Child, '19^). 



The susceptibility of tin- medusa bud, like that of the hydranth, 

 decreases with advancing development in all stages preceding 



