18 



The close affinities of the Protopteri and Lepidosirens cannot be denied. 

 If the observations which have been made on Lepidosiren are correct, the 

 result is then only to demonstrate that naturalists have placed too great 

 value on the partition of the heart. It is indeed certain that the presence 

 of two auricles is not even a positive character of the Amphibians. In 

 the genus Proteus, the heart is said, by Owen, to possess a single undivided 

 auricle, and he well remarks that " were even the septum auricula- 

 rum ' absent in the Salamander or Frog, these would not, therefore, be 

 Fishes. 



It would appear, then, that dmiht can not much longer be entertained of 

 the pertinence of the Lepidosirenoids f> the class of Fishes, or at least 

 to a class different from the Amphibians, if, with Professor Agassiz, we 

 should admit that four classes are confounded among the Fishes. The 

 more our knowledge of the anatomv of the Ganoids and the characteristics 

 of Fishes is increased, the stronger becomes the evidence of the relatio-8 

 of the Lepidosirenoids to Fishes. The analysis of Owen, and the preced- 

 ing remarks, will fully confirm the truth of this assertion. 



If the question of pertinence of those animals to the class of Fishes is 

 decided in the affirmative, there still remain to be discussed their position 

 in that class, and the station and rank to which they are entitled. 



Miiller has formed a distinct subclass which he has called Dipnoi, and 

 which is principally characterized by the presence of true scales on the 

 body, the possession of both lungs and gills, and the internal structure of 

 the bulbus arteriosus. Can this subclass be retained ? 



The similarity of the air bladder of the Polypteri to the pulmonary 

 eacs of the Lepidosirenoids hf.s been already commented on. There 

 seems to be no essential difference between the two, either anatomically or 

 physiologically. The branchial arches with their brancbise are alike present 

 in each, and although those of Lepidosiren are somewhat modified, they also 

 are essentially the same as in the Polypteri and the rest of the Ganoids, 

 The presence of cycloid scales is not decisive, for such are found to be 

 possessed by species of the genus Amia, and by other Cycloganoids. 



There is one difference, however, between the true Ganoids of Miiller 

 and his Dipnoi which is of considerable importance. The Ganoids have 

 been characterized by Miiller as fishes provided with numerous valves in 

 the arterial trunk. In this respect they differ from the Dipnoi. Professor 

 Owen has given the following description of the arterial trunk or bulbus* 

 arteriosus of the Lepidosiren annectens, or rather Protopterus anvectens : 



"This body presents externally a simple transversely oval form, but 

 its internal structure is more complicated than would be suspected from 

 its external appearance. It is formed by a short spiral turn of the dilated 

 aorta, which is concealed under a simple continuous outer fibrous coat ; 

 the area of this part of the vessel is almost entirely occupied by two con- 

 tinuous valvular projections, or their processes, which are attached by one 

 edge to the internal surface of the aorta, and have the opposite margin pro- 



