VARIATIONS IN OXYGEN TENSION. 



135 



tract to about -/$ of their former length and all motion ceases. 

 This contraction is followed by a slow relaxation and eventually 

 they are killed. But if replaced in sea water before death, they 

 slowly recover either completely or to a certain extent. The ratio 

 of those in motion to those still gives an index of the extent of 

 the injury. 4 



TECHNIQUE. 



The larvae being positively heliotropic, gather in great numbers 

 in the lighted side of the culture dish. A pipette-full (over 500 

 larvae) was taken and placed in a watch glass, then, as the larvse 

 collected again on the light side, the water could be tilted off, the 

 last traces being removed by blotting paper. They were next 

 washed twice with the solution to be experimented with and then 

 transferred by a pipette to 50 c.c. of that solution. Then at 

 hourly intervals about 100 larvae were removed from the test 

 solution, washed twice with sea water and replaced in sea water. 

 These \vere inspected one hour and in most cases also twelve hours 

 after their return to sea water. Fifty individuals were examined 

 and the ratio of those in motion to those still was determined. 



EXPERIMENTAL. 



I. The larva? were first exposed to 0.52 molecular NaCl in 

 almost complete absence of oxygen. The solution was boiled 

 while a stream of hydrogen was passed through, care being taken 



TABLE I. 



EXPERIMENT i. 

 Over 50 larvae examined in each case. 



Examined I Hour after Return to Sea Water. 



4 For a further description of the behaviour of Arenicola larvse in isotonic 

 NaCl see Lillie, R. S., Am. Jour. Physio!., 1909, XXIV., p. 14, and Am. Jour. 

 Physiol.. 1911, XXVIII., p. 210. 



