16 PALEONTOLOGY OF OHIO. 



It is an interesting fact that the living Dipnoans are inhabitants of the 

 Southern Hemisphere, while the living Granoids (as formerly defined) are 

 found only in the rivers of the continents lying north of the Equator. 

 This difiei-ence of geographical distribution, and the differences noticeable 

 in their anatomical structure, have led zoologists to place the Dipnoans 

 and Granoids in distinct orders; but Dr. Gunther proposes to unite them 

 in the order Ganoidei. The recent discoveries that have been alluded 

 to, seem to confirm this classification, by tracing the living Dipnoans back 

 to the Ganoids of the Palaeozoic ages, which then occupied both hemi- 

 spheres, and formed the most powerful and highly organized living 

 beings. 



The relationship which has been shown to exist between the Devonian 

 Ganoids and the modern Dipnoans suggests the question of the relative 

 grade of these ancient fishes ; for it is well known that the living Dip- 

 noans, from several points in their structure, and especially from the 

 possession of a three-chambered heart, and both lungs and gills, have 

 been regarded, first, as amphibians, and afterwards, as the highest 

 order of fishes. The terms high and low in classification, have been some- 

 what vaguely employed, and have created much misapprehension. They 

 are certainly not expressive of the true relationship between the synthetic 

 or generalized types of ancient times, and the more specialized of the 

 present. The modem Teleost is undoubtedly a more perfect finh than 

 any of the so-called fishes of the Palaeozoic ages, although the latter in- 

 clude in their structure certain points which link them more closely with 

 the higher classes, the Amphibia and Reptilia. In one aspect, therefore, 

 — their relationship to the higher groups^the earlier fishes were higher in 

 the scale than the more modern, but in other respects they were more rudi- 

 mentary in structure, for the vertebral column and brain-box were in them 

 cartilaginous, while in modern fishes they are ossified. The fact seems 

 to be simply this, that the great group of Ganoid fishes, which led and 

 gave character to the fauna of the Devonian age, formed the parent -stock 

 from which, by differentiation, the fishes have branched off on one side, 

 the amphibians and reptiles on another. In a tree the lower branches 

 may bear only leaves, and in that respect are but one step in advance of 

 the trunk, while the higher branches bear flowers and fruit ; but both 

 are outgrowths from the trunk, and fibres, reaching down from each, blend 

 there ; so that the trunk — low in position and function as it is — has more 

 in common with the branches which bear respectively the vegetative and 

 reproductive organs, than they have with each other. 



The mingling of amphibian and ichthyie characters in the ancient fishes 

 is readily explained — and we may say, can only be explained — by sup- 

 posing them to have formed the common stem from which both fishes 



