60 THE ORIGIN OF VERTEBRATES 



valuable than any other living vertebrate for the study of the stock 

 from which vertebrates sprang. 



Many authorities hold the view that the lamprey, like Amphioxus, 

 must he looked upon as degenerate, and therefore as no more suitable 

 for the investigation of the problem of vertebrate ancestry than is 

 Amphioxus itself. This charge of degeneracy is based on the state- 

 ment that the lamprey is a parasite, and that the eyes in Ammoccetes 

 are under the skin. The whole supposition of the degeneracy of the 

 Cyclostomata arose because of the prevailing belief of the time that 

 the earliest fishes were elasmobranchs, and therefore gnathosto- 

 matous. From such gnathostomatous fishes the cyclostomes were 

 supposed to have descended, having lost their jaws and become 

 suctorial in habit in consequence of their parasitism. 



The charge of parasitism is brought against the lamprey because 

 it is said to suck on to fishes and so obtain nutriment. It is, how- 

 ever, undoubtedly a free-swimming fish ; and when we see it coming 

 up the rivers in thousands to reach the spawning-beds, and sucking 

 on to the stones on the way in order to anchor itself against the 

 current, or holding on tightly during the actual process of spawning, 

 it does not seem justifiable to base a charge of degeneration upon a 

 parasitic habit, when such so-called habit simply consists in holding 

 on to its prey until its desires are satisfied. If, of course, its suctorial 

 mouth had arisen from an ancestral gnathostomatous mouth, then 

 the argument would have more force. 



Dohrn, however, gives absolutely no evidence of a former 

 gnathostomotous condition either in Petromyzon or, in its larval 

 state, Ammoccetes. He simply assumes that the Cyclostomata are 

 degenerated fishes and then proceeds to point out the rudiments of 

 skeleton, etc., which they still possess. Every point that Dohrn 

 makes can be turned round ; and, with more probability, it can be 

 argued that the various structures are the commencement of the 

 skeletal and other structures in the higher fishes, and not their 

 degenerated remnants. Compare the life-history of the lamprey 

 and of the tunicate. In the latter case we look upon the animal as 

 a degenerate vertebrate, because the larval stage alone shows verte- 

 brate characteristics ; when transformation has taken place, and the 

 adult form is reached, the vertebrate characteristics have vanished, 

 and the animal, instead of reaching a higher grade, has sunk lower 

 in the scale, the central nervous system especially having lost all 



