1 66 THE ORIGIN OF VERTEBRATES. 



all the text-books, but as an argument by analogy in favour of 

 the possibility of the original vertebrate having acquired his 

 new digestive outfit before the old one was absolutely function- 

 less in that respect, and having thus tided over a very pre- 

 carious period when it would have been very risky to have been 

 off with the old love before he was on with the new. 



The prececHng argument, based upon the first appearance 

 of the vertebrate in geologic time, is set forth by Dr. Gaskell 

 as follows : — 



" Before the highest mammal — man — appeared, the dominant race was 

 the mammahan quadruped, from whom the highest mammal of all — man 

 — sprung ; then comes in Mesozoic times the age of reptiles, which were 

 dominant when the mammal arose before them. Preceding this era we 

 find in Carlioniferous times that the amphibian was dominant, and from 

 them the next higher group, the reptiles, arose. Below the Carboniferous 

 comes the Devonian strata with their evidence of tlie dominance of fishes, 

 whence the amphibian was directly evolved. The evidence is so clear 

 that each succeeding higher form of vertebrate arose from the highest 

 stage reached at the time as to compel us to the conclusion that the 

 fishes arose from the race which was dominant at the time when fishes 

 first appeared. This brings us to the Silurian age, in which the evidence 

 of tlie rocks points unmistakably to the sea-scorpions (giant monsters, 

 some six feet long), king-crabs and trilobites as being the dominant race. 

 It was preceded by the great trilobite age, and the whole period from 

 the first appearance of the trilobite to the dwindling away of the sea- 

 scorpion may he designated as the Pal.neostracan age, the term Paljeostraca 

 to include both trilobites and the higher scorpion and king-crab forms 

 evolved from them. 



" The evidence of geology thus points strongly to the origm of the 

 vertebrates from the Palaeostraca arthropod forms which were not crus- 

 taceans and not arachnids,* but gave origin both to the modern day 

 crustaceans and arachnids." 



Dr. A. S. Woodward, who, in his address before the British 

 Association.! alludes to this passage in Dr. Gaskell's book, points 

 out that the true fish of the Devonian age had. most of them, 

 paddles which they used as crawlers as well as swimmers, dif- 

 fering in this respect from the typical fish. Moreover, as Dr. ~ 

 Gaskell shows, these fishes — Ptcraspis, Ccphalaspis, Ptcrichthys 

 — resemble, in a remarkable manner, members of the Palsos- 

 tracan group — Eiiryptcrus, Hcmiaspis, Phrxnns — so that it is 

 difficult to decide whether a fossil of wdiich tlie softer parts had 

 disappeared, was a fish with a head-shield, or an arthropod with 

 a carapace. 



Again, 



" fortunately there is still alive on this earth one member of this re- 

 markable group (of arthropods), the Limulus or King-crali. On the 

 vertebrate side the lowest non-degenerate vertebrate is the lamprey v/hich 

 spends a large portion of its existence in a larval stage. The value of this 

 fact will be seen." 



The bulk of the work is too technical for the layman, 

 although the information afforded by the excellent illustrations 



* Arachnids = scorpions, spiders, etc. 

 t At Winnepeg. 



