438 Simon Henry Gage 



p. 294). Of the European brook lamprey, Seeley ('86, p. 

 427). says that the dorsal fins may or may not be continuous. 

 He does not give the season when they are continuous and 

 when not so, but it may be inferred that they would be con- 

 tinuous in the spawning season and not in others, as with the 

 American brook lamprey. If the European and North Amer- 

 ican brook lampreys are really the same species, the distribu- 

 tion is remarkably wide, something as with the marine lam- 

 prey ; it is also apparently less susceptible to environment 

 than the marine lamprey, for it has apparently been practical- 

 ly unaffected by the special environment of the inland lakes. 

 Certainly also the conditions prevailing in the Mississippi 

 Valley must differ greatly from those found in Europe. 



SPAWNING AND THE STRUCTURAL MODIFICATIONS 

 PRECEDING IT. 



Structural Modifications. — Besides the change in the gonads 

 (ovary and spermary) there occur marked external and internal 

 changes. Among the most striking ot the internal modifica- 

 tions is the gradual change of the liver from the characteris- 

 tic hepatic color to a bright green. With some examples in 

 which the ova had not yet been shed, there were patches of 

 green intermingled with the ordinary liver color, but in all 

 the green color appears throughout the entire organ before 

 the spawning is completed. This green coloration of the 

 liver appears to be due to the occlusion of the bile ducts and 

 the retention of the katabolic products of the organ. In other 

 than the breeding season, green spherules of liquid of exactl)- 

 the same color may be found in great abundance in the termi- 

 nal third of the intestine. 



To the unaided eye the change in the liver is simply one of 

 color, but with the alimentary canal the striking change is the 

 diminution in size. From a tube 15 to 20 millimeters in diame- 

 ter in the lake lamprey, it atrophies to one of 4 or 5 millime- 

 ters or even less (PI. VII, fig. 27, 29, 31-32). The atrophy 

 takes place within two weeks, and begins at the terminal ex- 

 tremity, and extends gradually cephalad until the whole canal 



