33o LUNG-FISHES. 



earth-worms, and small fish given them, and then killing and eating each other, 

 making it difficult in the extreme to preserve the specimens. They are most 

 active at night, and appear to keep mostly to the shallow water, where they move 

 deliberately about on the bottom, alternately using the peculiar limbs of either 

 side, though their movements do not seem to be guided by any strict regularity. 

 Gray has compared these movements to those of a newt, and several other 

 observers have noticed them. The powerful tail forms a most efficient organ for 

 swimming rapidly through the water. It is well known that this fish comes to 

 the surface to breathe at short intervals, and thus it is evident that the lungs 

 perform an important, if not the chief, part in respiration during the active life of 

 the animal. The air passes out again through the opercular aperture, and the 

 movements of the operculum itself indicate the fact that bronchial as well as 

 pulmonary respiration takes place. Externally, the sexes present no characters 

 whatever distinguishing them apart. As in the American species, external gills 

 are developed in the young. As regards the breeding-habits of these fishes nothing 

 very definite is known. It is stated, however, that the numerous eggs and embryos 

 are carried about in an elongated gelatinous pouch attached to the sides of the 

 back of one of the parents, although the sex in which these receptacles are developed 

 does not appear to have been ascertained. In conclusion, it may be observed that 

 Professor Parker is of opinion that although the lung-fishes present certain 

 resemblances on the one hand to some of the sharks and ganoids, and on the other 

 to the lower Amphibians, yet they appear so distinct from both that he thinks 

 they ought to be removed from the fishes to form a class by themselves. 



Extinct In the Palaeozoic epoch lung-fishes formed an abundant group, 



Lung-Fishes, -which may be divided into three families. Of these the Carboniferous 

 and Permian Ctenoclontidce, as represented by Ctenodus and Sagenodus, resemble 

 the existing, forms in the absence of marginal teeth to the jaw and of jugular 

 plates on the throat, but differ by the numerous membrane-bones of the skull ; the 

 caudal fin being of the fringed type, and the scales cycloidal. The type genus, 

 which includes species of 5 feet in length, takes its name from the comb-like 

 structure of the ridged palatal teeth. The second family, Phaneroprteuridce, differs 

 from the last in the presence of both marginal teeth and jugular plates ; the 

 typical genus Phaneropleurum, including small species from the Devonian. In 

 the Dipteridce, as represented by the Devonian Dipterus and Palcedaphus, jugular 

 plates are present, but there are no marginal teeth, and the tail is of the hetero- 

 cercal type ; the skull having numerous membrane-bones. The teeth are very 

 similar to those of the Australian lung-fish, but may be ornamented with small 

 ridges and pustules. 



The Berry-Bone Fishes. — Order Arthrodira. 



The extraordinary Palaeozoic group typically represented by the berry-bone 

 fish (Coccosteus) of the Scottish Devonian differs from the true lung-fishes in that 

 in place of scales the fore-part of the body is protected by large bony plates, of 

 which one pair is articulated by a hinge to the hinder-part of the skull, which is 

 likewise invested with bones bearing a similar pustular, or berry-like sculpture. 



