94 



VERTEBRATE ZOOLOGY 



15. The eggs are comparatively small and with little yolk. Cleav- 

 age is holoblastic. The larva has a long life and undergoes a radical 

 metamorphosis into the adult state. 



Thus the lampreys may be considered as a step in advance of the 

 hags in numbers 1, 2, 3, 4, 5, 6, 8, 10, 11, 13, 14. In other respects 



FIG. 50. Spawning of the Brook-Lamprey (Petromyzon wilderi). On the right 

 of the figure a male is attached to the head of a female. (From Cambridge Nat. 

 Hist., after Dean and Summer.) 



they show either more primitive conditions or merely different ad- 

 aptations for their totally different life. 



J Life Cycle of the Lamprey. The lamprey breeds in fresh water, even 

 in the case of the marine forms. The male coils the tail about the 

 body of the female in the spawning act (Fig. 50) and,during a vigorous 



