THE EVOLUTION OF FISHES. 557 



has no hard parts, no bones, nor teeth, nor scales, nor fins, no traces 

 of its kind are found among the fossils. If the primitive lish was like 

 it in important respects, all record of this has necessarily vanished from 

 the earth. 



The next group of living fishes, the Cyclostomes, including the hag- 

 fishes and lampreys, — fishes with small skull and brain but without 

 limbs or jaws, — stands at a great distance above the lancelet in com- 

 plexity of structure, and equally far from the true fishes in its primitive 

 simplicity. In fact the lamprey is farther from the true fish in struc- 

 ture than a perch is frcon an eagle. Yet for all that it may be an 

 offshoot from the primitive line of fish-descent. There is not much in 

 the structure of the lamprey which may be preserved in the rocks. But 

 the cartilaginous skull, the backbone, fins and teeth may sometimes 

 leave their traces in soft clay or lithographic stone. These parts are 

 actually represented in a fossil form bearing some likeness to a lam- 

 prey found in the Devonian of Scotland known as Falceospondylus. 

 This early form was a highly specialized one with well-defined verte- 

 brae, a fact which shows that the group had reached a relatively high 

 development even in these early times. The few existing Cyclostomes 

 may even be looked upon as degraded types as compared with their 

 Devonian ancestors. 



Besides the lampreys the Devonian seas swarmed with mysterious 

 creatures covered with a coat of mail, fish-like in some regards, but 

 limbless, without true jaws and having next to nothing in common 

 with the fishes of to-day. These are called Ostracophori, and most 

 recent authorities, as Woodward and Dean, are inclined to regard them 

 as highly modified or specialized lampreys, a side offshoot which has 

 left no descendants among recent forms. Cope has compared these 

 Ostracoderms to the larva of Tunicates, and Patten has suggested their 

 affinity to spiders, or rather to the horseshoe crab (Liniulits), which 

 is at least as much spider as crab. The weight of evidence would rather 

 place them nearest the lampreys, but certainly not in the same natural 

 class. 



Among these forms in coat of mail are some in which the jointed 

 and movable angles of the head suggest the pectoral spines of some cat- 

 fishes. But in spite of its resemblance to a fin, the spine of the pectoral 

 fin in Pterichthys is an outgrowth of the ossified skin and has no more 

 homology with the spines of fishes than the mailed plates have with 

 the bones of a fish's cranium. In none of these fishes has any trace 

 of an internal skeleton been found. It must have retained its primitive 

 gelatinous character. There are, however, some traces of eyes, and 

 the mucous channels of the lateral line indicate that these creatures 

 possessed some other special senses. 



Whatever the Ostracophores may be, they are not true fishes and 

 they should not be included within the much-abused term Ganoidei, 



