The Primitive Fishes 259 



All are agreed that the cyclostomes are the most primi- 

 tive of the true fishes. Some zoologists have held that they 

 are degenerate derivatives from some of the higher fishes, 

 but such is absolutely contrary to all structural, physiologi- 

 cal, taxonomic and developmental evidence. Through com- 

 mencing epizoism and — as in Myxine — through ultimate 

 endoparasitism, a few degenerate characters are shown, 

 but these are by no means profound. From the progressive 

 evolutionary standpoint they should have been evolving 

 in early or mid Cambrian time; and from action of the 

 great biological law of "preclimax, climax, and anticlimax" 

 that the writer considers to appear all along the line of 

 organic development, they should have reached a biological 

 climax in size, structure, abundance, and wide distribution 

 from early Silurian to late Old Red time. The anticlimax 

 would progress slowly through Carboniferous to Permian, 

 possibly even to Triassic time, and thereafter only lingering 

 remnants might be left. 



Such an evolutionary history runs exactly parallel to 

 the knowledge we have of conodonts. Now it may be said 

 that traces of conodonts should appear in strata from 

 Triassic to recent times, if they truly are cyclostome teeth. 

 But the comparative rarity and localized distribution of 

 the species and genera of cyclostomes now, indicates that 

 a restricting and destructive action has gone on for at least 

 considerable geologic time amongst the group. 



Shortly then we would sum up by saying: (i) that the 

 probability of conodonts being crustacean gastric or mandi- 

 bular teeth is most unlikely, or even impossible, alike from 

 variety, structure, and the absence of crustacean remains 

 then, to which such would belong. (2) They are, for much 

 the same reasons not likely to be annelidan teeth, as along- 

 side them might be expected the typical setae that do not 

 appear. (3) Annelidan teeth are simple pointed tearing 

 structures, conodonts show great diversity of shape and 

 structure. (4) The shapes of conodonts and of cyclostome 

 teeth very closely agree, and differ from the teeth in the 

 other groups to which they have been assigned. (5) The 

 abundant occurrence of conodonts in Siluro-Devonian 

 strata, is evolutionarily in keeping with their being of cyclo- 



