The Lake and Brook Lainpreys of New York 465 



from tlie gills. The forward movement is not so great, how- 

 ever, as might be expected from the strength of the backward 

 current, and the slight retardation due to the friction of the 

 bottom of the vessel. ' While the animal is lying on its side, 

 the current into the mouth is clearly seen by dropping a little 

 starch into the water. The currents can also be very satisfac- 

 torily studied by placing the animal in a test-tube or narrow 

 jar with water and a little corn starch. 



Whenever the head of the larval lamprey can be seen in a 

 good light, an arched, reddish, moving body is visible through 

 the translucent bod}' wall between the opening of the mouth 

 and first gill. This is in rhythmical motion toward and away 

 from the mouth. It is the velum ^ composed of two symme- 

 trically placed, arched curtains which perform the double 

 function of valve to prevent the water from going out through 

 the mouth when the branchial apparatus is constricted, and 

 also of moving by its own musculature something as the dia- 

 phragm of a mammal and thus alternately increasing and di- 

 minishing the size of the branchial cavity. If the movement 

 is carefully watched and compared with the alternate con- 

 striction and expansion of the branchial apparatus, it is seen 

 that the expansion of the branchial apparatus and the ce- 

 phalic or forward movement of the velum coincide, both thus 

 acting to increase the size of the branchial chamber and there- 

 fore to draw water into the branchial cavity,' that is, both are 

 inspirators. On the other hand, in expiration the vekmi is 

 drawn caudad at the same time that the branchial chamber is 

 constricted and thus a double diminution of the capacity of 

 the branchial chamber results and the expiration is complete. 

 This caudal movement of the velum has also tended to draw 

 water into the space between the velum and the sieve like 

 tentacles. This water is drawn into the branchial chamber 

 immediately upon the expansion of the branchial chamber and 

 the forward movement of the velum. Owing to the valves 

 over the branchiopores, the branchial chamber can only be 

 filled through the mouth, and a current .is drawn into the 

 mouth both in expiration by the caudally moving velum, and 

 in inspiration by the expanding branchial chamber, hence it 



