770 



MR. E. S. GOODRICH OK 



[Nov. 12, 



at once be determined by an examination of its scale. Doubtless, 

 all the types have been evolved from some common ancestral 

 scale, and numerous intermediate forms will be found, whose 

 position will be difficult to assign; but so far the chief types 

 remain remarkably distinct from each other. * 



The Scale 0/ Polyptebus. — Let us now apply our test to the 

 scale of Polypterus. The Polypterini have always been placed 

 among the so-called Crossopterygii ever since Huxley wrote his 

 famous paper on the classification of Devonian fishes (8). I 

 have elsewhere discussed in greater detail the affinities of Poly- 

 pterus (4) ; and shall only mention here that, in a j)aper published 

 some years ago (4 «), my opinion has already been expressed 

 that its relationship is rather with the Actinopterygii than with 

 extinct " Crossopterygii." 



The scale of Polypterus has been described by Agassiz (1), 

 Leydig (12), and Hertwig (7). The last author especially 



Text-fig. 203. 



(From Lankester's ' Treatise on Zoology,' by permission of Messrs. A. & C. Black.) 



Portion of a thick transverse section of the scale oi Folypterus hiehir Geoffr., much 

 enlarged, h., inner bony or isopedine layer ; c, canaliculi of the cosmine layer ; 

 d., superficial denticle ; g., gauoine layer ; h., system of horizontal vascular 

 canals; o., opening of vertical canal on outer surface ;'«e., vertical canal. 



has contributed much information concerning the histological 

 structure of the scale itself, and the denticles which become 

 attached to its surface (p. 763). 



A glance at text-fig. 203 will show at once that the scale of 



* Since this was written I have found a paper, which unfortunately escaped my 

 notice, by Dr. H. Scupin (" Zur Histologic der Ganoidschuppen," Arch. f. Naturg., 

 vol. Ixii. 1896), in which the microscopic structure of fish-scales is dealt with. 



