RESPIEATION OF DYTISCUS MARGINALIS L. 



343 



bubble and the water, ^^ and after a sample has been taken of the 

 air with one of the pipettes, C, D, and E. These pipettes are 

 built exactly hke the ones described by Krogh. Care should be 

 taken not to make them too long. After breathing, another 

 portion is taken, and quickly the analysis is made, first of the 

 third one, because the air is not in equilibrium with the water, 

 afterwards of the control portion. 



Fig. 3. Apparatus for the stud}" of the expired air of Dytiscus. By moving 

 a water-filled funnel connected with B upwards, the air of the bubble A is pressed 

 into the space F, whereas the superfluous water escapes at the rim. The animal 

 is allowed to breathe in the space F. With the pipettes C, D, and E (D and E 

 have been indicated with a broken line, as they do not lie in the plane of the 

 picture) we can at every movement get a sample of the air. 



With this little apparatus I obtained the following results with 

 regard to the composition of the air before and after breathing 

 (the analysis has again been made with Krogh's micro-gas analy- 

 sis apparatus) : 



13 It is very easy to prevent the animal from breathing for a while by shaking 

 the beaker at the very moment when it intends to open its cleft for this purpose. 



