IO2 JEAN DAWSON. 



In order to learn how the animal detaches itself the following 

 observations were made : The ectal and ental valves of the ex- 

 ternal branchiopore were watched very closely with a lens to de- 

 termine their action, if any, at the moment when the animal de- 

 tached itself. This proved to be no easy task since the valves were 

 found to act so quickly that one could see but a flash of white 

 in the dark gill opening and the animal was gone before one 

 could see what had happened. This difficulty was greatly les- 

 sened by the use of a small amount of chloretone in the water. 

 This increased the rate of breathing at first but then gradually 

 lowered it so that one could more easily tell what was taking 

 place. 



The cephalic and caudal sides of the gill opening were seen 

 to be approximated so that instead of remaining circular, as dur- 

 ing ordinary respiration the opening became elliptical with its 

 longest axis dorso-ventral. Thus the ectal valve was stretched 

 taut. The ental valves could be seen to come together so as to 

 close this gill opening. Almost the instant the valves closed, 

 the animal detached itself. 



It thus appears that the valves of the external branchiopore, 

 act in the manner indicated by their structure, to close the bran- 

 chiopore at the moment when the animal detaches itself. Ex- 

 periments were now tried to see if the water was sent to the 

 mouth cavity to destroy the vacuum as it seemed from a knowl- 

 edge of the workings of the valves and their action at the mo- 

 ment of detachment of the animal that it might be. 



Experiment i. The head of a lamprey while attached to the 

 side of a glass dish was gently pushed up out of the water without 

 detaching the animal. Care was taken to thoroughly dry the 

 the glass around the oral funnel. When the animal detached 

 itself, water was seen to run down the side of the dish from the 

 mouth. 



If the lamprey's head and several gills were thus lifted above 

 the water, air bubbles and water are expelled from the mouth 

 upon the animals detaching itself. The air bubbles must have 

 been taken in through the gill openings which were above the 

 water and must have passed forward through the water tube and 

 pharynx into the oral funnel. 



