THE AXIAL GRADIENTS IN HYDROZOA. 177 



found by preliminary experiment to inhibit development to a 

 greater or less degree but not to be directly lethal. Agents and 

 indicated concentrations used are as follows: KCX, ;;: 2<>< 



5000, m/ 50000; HC1, pH 6.8 , pH 7.2, pH 7.3, pll 7.4+;" 

 LiCl, m 25, /;; 50, m .80, w/i6o; ethyl urethane, >;/.':? 5 and very 

 dilute neutral red. All solutions were made up in sea water and 

 the ( -om entrations given are those indicated by amour. .-m 



and volume of water used. For experiment finger bowls holding 

 SOUK- ;.., , . re used. These could be brought under a bin- 



ocular <>i evtn under low power of a compound micro-cope 

 without remo\al or disturbance of the developing material. 

 \\'heu volati'. . -,s were used bowls with an >od 



contact \\ith -, plate were selected, l>ein;^ completely tilled 



with the Dilution and covered with the plate -.chide air. 



Atmo-pheric humidity being high, there \vas practically no lo-- 

 of u ater uiidi-r these conditions and certainly no appreciable \< >ss 



it Cilice renewal was usually made daily. 



The variations in experimental procedure may be grouped as 

 follow-: (a) continuous e.\[>osure to a certain concentration 



lining \\ith the earliest stages obtainal''' temporary 



cxpo-nre to a certain concentration beginning with the earlie.-t 



followed by lower concentration or by return to M -a v\at<-r ; 



rly ile\elopment in sea water, exposure to a^ent beginninv; 

 at later stage t-lastula, early planula). 



I'he developmental stages of Phialidiuti: ;>til'le to 



change in mdition that some degree of de\ 1 1< pmental moditK a- 

 tion liccjui-ntK 01 urs in sea water in the laboratory if condition^ 

 not maintained near the optimum. For example, if the 

 developmental >tages remain too long in the container witli 1 

 numbei> of medusa,', differential inhibition ot development 

 n--ult>, the modifications bring similar to tho-e induced by other 

 mean-. I'mler these conditions there i- a decrease in pH, 

 re-nltin;c \\lv\\\ from the CO 2 production of the medu-a-. There 

 may also be >ome accumulation of Other metabolic product- and 



1 At the time ti timents were performed it was 1 increase 



in ll-ion concentration was the chief inhibiting factor in the acid experiments, but 

 in tin- li^lit <>f the recent w<>rk of Smith and Clov. . it appears probable that 



tlie increase in O mm the addition of HC1 to sea water is more imi -i fant 



than the in. H-ion concentration. In my experiments no attempt was 



made to determini after addition of HC1. 



12 



