RESPIRATION IN WATER 



37 



of pleopods. The frequency of this beating has been studied 

 repeatedly (F. Peters, 1938; Fox and Johnson, 1934), and 

 Lindroth (1938.1) succeeded in placing a crayfish so that the 

 flow could be measured (Fig. 12). 



The curve, Fig. 13, shows the effect of oxygen concentration 

 upon the ventilation. At high oxygen concentrations in the 

 water down to about atmospheric tension the effect is slight 

 only, but at lower concentrations the ventilation rises abruptly, 

 and the animal is characterized as dyspnoeic when the exertion 



kzzzzzzzzzzzzzzzz; 



V///.V/ /////// / Z Z? 



Fig. 12. Determination of ventilation in the crayfish. A, box with one 

 rubber wall; B, fixation plate; C, connections to flow meter; D, aeration. 

 (Lindroth.) 



of breathing is a conspicuous item in the general behaviour. 

 It is a very characteristic feature that the utilization of the 

 oxygen is only slightly reduced in dyspnoea. In one case, 

 for instance, the oxygen concentration was reduced in the 

 passage through the gill chamber from 6.68 ml/1 to 2.03 when 

 the ventilation was 6 ml/minute, a utilization of 70%, while 

 in another with a ventilation of 16.5 ml/min it was reduced 

 from 2.10 to 0.86, a utilization of 59%. Somewhat lower 

 utilizations, 49% on an average, were observed by Hazelhoff 

 (1938) on a number of marine Crustacea. 



