The Lake and Brook Lampreys of New York 467 



the course of the water in its passage through the branchial 

 apparatus. 



With larvae in confinement, whenever the water is in- 

 sufficiently aerated, the head and sometimes the whole 

 branchial apparatus is projected from the burrow into the 

 water. If the water is changed they disappear in a short 

 time. If the water is not changed or aerated in someway the 

 larva will leave its burrow entirely and make violent efforts to 

 escape from the vessel. If one watches the indications he 

 soon learns about how often to change the water ; in any case 

 he knows that the water must be aerated or changed when- 

 ever the larvae give this sign of beginning suffocation. 



Respiratory Mechanism in the Adult. — On the change from 

 the larval to the adult form, the food changes from minute 

 organisms filtered from the water to blood sucked from other 

 fishes, and the mode of inspiration must necessarily change ; 

 for when the lamprey is attached for the purpose of obtain- 

 ing food or for any other object, there is no possibility of 

 inspiring water through the mouth. When unattached, how- 

 ever, water may still be taken into the branchial cavity 

 through the mouth. For a considerable time during trans- 

 formation and even when the tongue and the mouth have 

 nearly assumed the mature condition, if one watches the 

 particles in the water it is seen that there is still an almo.st 

 constant stream flowing into the mouth. Later, however, 

 although water may enter the mouth in respiration, it does so 

 rarely, but on the contrary both inspiratory and expiratory 

 streams must pass in and out of the branchial chamber 

 through the branchiopores. 



As shown in figure 52 of PI. VIII, the branchiae of the 

 larva appear to project freely into a common branchial cham- 

 ber, although there are seven openings on each side from this 

 chamber. In the adult, on the other hand, there are seven 

 gill pouches on each side, each pouch being independent ex- 

 cept for a small opening into the greatly constricted bron- 

 chus ; and, as stated above, the respiratory streams are both 

 in and out of each branchiopore so that if the bronchus were 

 entirely occluded and part of the gill pouches obliterated, 



