SCOTT, STUDY OF CHANGES IN MUSTELUS CAN IS 



57 



in intensity and frequency until nearly an hour after immersion, and 

 then gradually and irregularly declined in number and strength. These 

 respiratory movements are possibly modifications of increased intensity 

 of the normal gill-cleaning movements mentioned above. It is also pos- 

 sible that both have fundamentally the same cause but that the stimulus 

 is more intense when the fish is immersed in fresh water. Foreign ma- 



tM:'^-:;!.:'|ri, 



Fig. 11. — Showing the change in the character of the respirations during an hour after 

 immersion of Mustelus in fresh tcater. Irregularities represent spasmodic respira- 

 tory movements. 



terial on the surfaces of the gill membranes prevents the normal func- 

 tioning of these structures and tends toward asphyxiation. The changes 

 in the gill membranes brought about by immersion of the fish in fresh 

 water are accompanied by the same convulsive gill movements. 



There is considerable variation in the respiratory modifications in 

 individuals, but the above mentioned features were observable in most 



