BREATHING MECHANISM OF THE LAMPREYS. 1 03 



Experiment 2. A thin mixture of carmine and water was in- 

 troduced into a gill of a L. wilderi attached to the side of a glass 

 dish, by placing the end of a pipette over the external branchio- 

 pore and gently but steadily pressing the bulb. The animal ex- 

 pelled the carmine from the gill opening with violence. When a 

 thicker mixture was used, the animal made a great effort to ex- 

 pel it, but when the carmine was still steadily poured into the 

 gill, the animal detached itself and a stream of red was seen to 

 issue from the mouth. When carmine was seen to issue from the 

 mouth, no carmine issued from the gills, thus showing that the 

 valves were acting to close the external branchiopore and to 

 cause the water to take a forward course so as to make detach- 

 ment easier for the lamprey. These experiments seem to leave 

 no doubt that detachment is effected in Lampetra wilderi by a 

 current of water forced from the gill sacs into the mouth cavity 

 and that this is rendered possible by the closure of the external 

 branchiopore by its valves. 



As far as I have been able to find, the valves of the external 

 branchiopore are mentioned by but two writers. 



Mayer (1835) speaks of two flaps at the external branchiopore 

 and describes them as being swept out and in through thf 

 branchiopore by the respiratory current. He assigns no function 

 to them except that of forming a tube for the outflowing water. 



Gage (1893) says: " In the case of the lamprey one might 

 think at first that no valves were necessary in respiration, for if 

 the branchial pouches are open to the surrounding medium 

 through the branchiopores any enlargement of the branchial 

 spaces would cause the water to enter, and conversely, any con- 

 striction would empty the branchial sacs. This view is correct 

 but this mode of simply drawing water into a sac and expelling 

 it has not apparently answered the requirements of the lamprey, 

 and there is present the thin valve (the ectal valve) which covers 

 the entire branchiopore in the larva, and in addition a double 

 valve (ental valve), which is formed by the growth and modifica- 

 tion of the middle gill lamella of the caudal half of the branchial 

 sac." Concerning the function of the valves he says: "In in- 

 spiration the two parts of the inner or ental valve turn away from 

 each other and are pressed toward the cephalic wall of the 



