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 be 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 Ammoceetes 
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 
