PROCHORDATA AND CYCLOSTOMES 



327 



From "Animate Creation" 



FIG. 119. Lampreys. 



round mouth acts as a sucking disk, and enables the 

 lamprey to hold on to the side of a fish, while it rasps 

 the flesh with its horny teeth. Fishes with soft scales 

 are most likely to be attacked, and dense, hard scales 

 serve as a protection. The hagfishes, which are marine, 

 actually burrow into the bodies of fishes and become 

 parasitic. In very ancient rocks in Scotland there 

 has been discovered a small fossil animal which in 

 many ways resembles the cyclostomes, having a skull 

 but no jaws or limbs, but possessing distinctly formed 

 vertebrae. This extinct form, known as Palceospon- 

 dylus, suggests that the cyclostome type is a very old 

 one, although we know next to nothing about its history. 

 The hard, porcelainlike scales of many ancient fishes 

 may have been developed partly as a protection against 

 these predatory creatures. 



