41 8 HENRY C. TRACY. 



in the case of the higher concentrations, the respiratory rate 

 rises above the normal on return to normal sea water. 



Obviously there is a close similarity between the effect of 

 CO 2 on the rate of movements of the body and rate of respiratory 

 movements in the lower concentrations; in the higher concen- 

 trations the respiratory mechanism has a compensatory capacity 

 both during exposure and in recovery afterward, which is not 

 possessed by the motility mechanism. Apparently, then, the 

 regulation of respiration and motility at ordinary concentrations 

 of COo takes place through similar mechanisms; in high concen- 

 trations, the respiratory system can bring into play secondary 

 reserve mechanisms, which appears to be beyond the capacity 

 of the system controlling body movements. 



The resistance of these larvae to asphyxiating conditions is 

 very great. One of these larvae was left over night in a bottle 

 containing the highest concentration of CO 2 ; the next day the 

 specimen lay motionless on the bottom of the bottle with the 

 respiratory rate about the same as shown on the preceding day; 

 on putting the specimen into fresh sea water the respiratory rate 

 quickly jumped above the normal, the body movements ap- 

 proached the normal in 12 to 15 minutes. Larvae placed in 

 water from asphyxiated Fundulns (which causes acute symptoms 

 in half grown adult toad fish) apparently suffered no inconven- 

 ience; in boiled sea water, through which hydrogen had been 

 bubbled for one and a half hours, the early larva? show no effects 

 during the first hour and a half (aside from reduction of body 

 movements) although oxygen was entirely absent. Evidently 

 anaerobic respiration is possible for a considerable time at least, 

 in these embryos. 



Stockard ('21, p. 173) indicated the probability that double 

 and abnormal embryos in fishes may be produced by asphyxial 

 conditions at certain stages. In the toad fish I have found only 

 one double larva, although in the course of several seasons I 

 have examined several thousand specimens. This high degree 

 of resistance to asphyxial conditions is no doubt correlated with 

 the crowded stagnant condition of the water in which this species 

 passes its embryonic and larval life. 



That there is some definite relation between spontaneous 

 movements and respiratory movements is shown by the reduction 



