BREATHING MECHANISM OF THE LAMPREYS. IO5 



experiment, the inflowing stream may indeed be directed toward 

 the center of the gill sac by the ental valve, but when the gill sac 

 begins to empty itself the ental valves respond to the slightest 

 current, the branchiopore is unobstructed and all the water 

 within the gill sac is equally free to pass out through it. It 

 would seem that the water should then flow directly out 

 through the branchiopore rather than that it should take the cir- 

 cuitous course between the gill lamellae into the smooth channel 

 along the dorsal and ventral borders of the gill sac and thence out. 



D. The Velar Jaws. Mayer (37) gives a figure in which the 

 velar jaws are shown, but gives no description of them. 



Stannius (1840) speaks of thread-like projections from the car- 

 tilage of the velar valves and may thus possibly refer to the velar 

 jaws. 



Vogt and Yung (1889) described the velar jaws as a straining 

 apparatus. From the cartilages of the valves "extend five long 

 thin forked points directed forward with their converging ends 

 and thus a strainer is formed which opposes the entrance of 

 bodies from the pharynx." 



I have examined the velar jaws of many specimens of P. inari- 

 nus but have never seen them with projections or otherwise than 

 smooth. That the jaws would act as a strainer and serve to 

 hinder the entrance of foreign bodies into the water tube is clear 

 from their position. From the fact that they close when the 

 velar valves close, it is clear that they may seize and hold foreign 

 bodies which are being carried into the water tube. If the velar 

 valves should then open to permit the forward current from the 

 water tube to enter the pharynx, the velar jaws would be opened 

 by the same muscular contraction, the foreign body would be re- 

 leased and swept forward out of the mouth. 



Nevertheless pending the examination of stomach contents the 

 question as to what extent, if at all, the lamprey takes food by 

 means of a current of water entering the mouth must be regarded 

 as still open. If food is thus taken, it is quite possible that as 

 food particles are swept past the velar jaws into the water tube 

 the jaws may seize the larger particles, permitting the smaller 

 ones to pass on with the inspired water. The closure of the jaws 

 would be accompanied by the closure of the velar valves and the 



