522 CYCLOSTOMATA. 
The spawning takes place in spring, usually far up rivers. 
Before laying the eggs, the lamprey seems to fast (cf. 
i, 
yf 
Fic. 276.—The lamprey (Petromyzon marinus). 
I, The entire animal ; note the seven gill-slits of which the first is 
marked g.s., the nostril #., and the unpaired median fins. 
II. Ventral pee of the head ; 2.2. pest teeth; 22, lower 
teeth; ., the piston in the mouth. 
Uppers surface of the 
head ; z., the nostril with the pineal Bi be 
‘ind it ; ¢., the eye. 
salmon, Protopterus, frog), and its muscles undergo a 
granular degeneration (cf. Protopterus, tadpole, etc.). Soon 
