THE PHYLA HEMICHORDATA AND CHORDATA 



Fig. 18.11. Primitive fishes, living and extinct. A, Polyptems, the "bichir," one of the 

 most primitive of existing ray-finned fishes. B, Lepidosteus, a gar pike, and C, Scaphyrhynchiis, 

 the shovel-nosed sturgeon; these are less ancient but comparativelv primitive ray-finned types. 

 A restoration of Cheirolepis, one of the first of the ray-finned fishes, which flourished during 

 the Devonian period. E, restoration of the lobe-finned fish Eusthenopteron, which also lived 

 in Devonian times but which appears to have been closer to the line of fishes ancestral to later 

 tetrapod types. (.4, B, and C, photographs courtesy New York Zoological Society; D and E, 

 from paintings by F. L. Jacques, courtesy American Museum of Natural History.) 



all the most familiar fishes of fresh and salt water, such as trout, salmon, 

 carp, bass, perch, catfish, cod, herring, mackerel, and many others. Although 

 they are all modifications of the ray-finned type of fishes, the diversity of 

 these forms is amazing. Almost every kind of shortening, lengthening, and 

 flattening can be found in one species or another, along with such extreme 

 modifications as those of the pipefish, toadfish, seahorse, flying fish, flounder, 

 and the luminescent fishes of the depths of the ocean. 



The Pisces, living and extinct, are thus the basic type among vertebrate 

 animals. Appearing first in the fossil record, they include at the present 

 time descendants of Devonian types, such as sharks, which are flourishing if 

 not large groups, as well as groups living and extinct that suggest the be- 

 ginnings of vertebrate life on land. Originating in fresh water, as the 

 fossil record indicates, the Pisces have invaded the ocean and since that 

 time have inhabited both fresh and salt water. The story of the ancient lung 



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