INTRODUCTION. 3 



naked skin, would be set aside in spite of the Ganoid character of their heart, intestine, 

 and optic nerves. Batistes, Loricaria, and a number of Plectognathous fishes would 

 enter the order, entitled to do so solely by their osseous scutes. The zoologist cannot 

 tolerate any principle of division which involves such separations and combinations as 

 these. 



Muller has pointed out how destitute of value is any classification of Teleostean fishes 

 based upon scale characters. Well-defined and natural families contain both cycloid and 

 ctenoid genera. Genera can be named with both cycloid and ctenoid species. Atherina 

 (the Sand Smelt) and Muyil (the common Mullet) both belong to one family, the 

 Mugilidce, yet the first is cycloid and the second ctenoid. The families Percidce, 

 Chpeidce, Gobidce, and many others include both forms. Thus, the Scombrida, ranked 

 by Agassiz as cycloid, contain such genera as Nomeus, Cubiceps, and Neptonemus, which 

 are truly cycloid, while Platystethus is ctenoid, and Pelamys Sarda both ctenoid and 

 cycloid. In short, scale-characters tell us nothing unless the affinities of the fish in 

 question are beforehand nearly determined. 



In 1 844 appeared the celebrated memoir of Muller, ' Ueber den Bau und die 

 Grenzen der Ganoiden/ 1 a work which marks the era of sound general principles of 

 definition and classification of Ganoid fishes. The author gives first a historical resume 

 of the work done by his predecessors in this field of inquiry, Rafinesque, De Blainville, 

 Cuvier, and Agassiz. The views of the last only of these receive a full discussion, for he 

 alone had recognised the ties which connect the Ganoids together. Briefly, but with 

 irresistible weight of argument, Muller disposes of the arrangement based upon scale 

 characters. He points out the many fatal anomalies which result from the definitions of 

 orders according to Agassiz, and shatters all hope of establishing a natural history upon 

 such easy distinctions. The essential peculiarities of the Ganoids are shown to lie, not 

 in scales, fins, or tail, but in the heart, brain, and intestine. 



The anatomical research of this essay gives it a permanent value which the labours of 

 no mere systematist can confer. The structure of Polypterus and Lepidosteus in particular 

 is given with a fulness and completeness which more recent investigation has hardly 

 modified. In the reconstruction of the order certain of the Siluroids, Scleroderms, 

 Gymnodonts, and Lophobranchs, admitted by Agassiz as armour-plated fishes, are 

 removed entirely from the order Ganoidei. The remaining recent genera are enumerated 

 by Muller thus : Lepidosteus, Polyjrferus, Acipenser, Scaphirhynchus, and Polyodon. 



Since 1844 the list of genera has been modified as follows. The Ganoid structure of 

 Amia, discovered by Vogt, is announced in a postscript to Muller's paper. Calamoichthys, 

 first described in 1865, and Ceratodus, added to the list of living genera in 1870, were 

 unknown to Muller. Lepidosiren and Protopterus, excluded by Muller, it is now 



puzzling to the pure zoologist, is most interesting and suggestive to those who seek to infer biological 

 principles from the results of zoology. 



1 ' Abhandlungen der Akademie der Wissenschaften zu Berlin,' 1844. 



