420 HENRY C. TRACY. 



ments since the results suggest that endogenous movements 

 may be stimulated by variations, local as well as general, in the 

 concentration level of metabolites which result from differences 

 in the metabolism rate in different regions of the embryo. Jacobs 

 ('22, p. 25) has made a similar suggestion regarding the produc- 

 tion of pseudopods in Amoeba. 



SUMMARY AND CONCLUSIONS. 



1. Xewly hatched and free swimming larvae of toad fish 

 (Opsanus tan] were subjected to different concentrations of COo 

 produced by additions of different percentages of HCL n/2O to 

 sea water. 



2. Increased concentration of COz is followed by an increase 

 in the endogenous (spontaneous) body movements in both 

 stages; in newly hatched larvae the reaction of COa is less intense 

 but of greater duration (average about 25 minutes) than in 

 free swimming larvae (average about 10 minutes). 



3. On return to normal sea water from the higher concentra- 

 tion of CO, the frequency of the body movements is depressed 

 below the normal; the depression is less in the newly hatched 

 larvae than in the free swimmer and the recovery is slower. 



4. In the lower ranges of COo concentration, the body move- 

 ments (in both stages) and the rate of respiratory movements 

 (free swimmers) vary with the increase in CO 2 ; in the higher 

 ranges the body movements, after a period of stimulation, 

 remain depressed far below the normal, while the respiratory 

 movements, after a brief stimulation followed by depression and 

 irregular rythm, recover and proceed regularly at a little below 

 the normal rate. 



5. On return to normal sea water, the body movements for 

 all concentrations of COo remain depressed (about 30 minutes 

 for the free swimmers, longer for the newly hatched larvae) ; 

 the rate of respiratory movements is below the normal for the 

 lower concentrations, but is increased above the normal on 

 return from higher concentrations. 



6. Respiratory movements and spontaneous body movements 

 react similarly to the lower concentrations of CO 2 and hence 

 their regulation probably takes place through a similar mech- 

 anism; at the higher concentrations, the respiratory system 



