VI 
THE LUNG-FISHES 
LUNG-FISHES, or Dipnoans, have long been looked upon 
as the linking type between amphibians and fishes. In 
some regards of structure they approach the primitive 
sharks ; in others, they resemble so closely the salamanders 
that they were recently regarded by W. N. Parker as worthy 
of a class by themselves, intermediate between fishes and 
amphibians. As with the Chimzeroids, their few surviving 
members give but a mere suggestion of the former size 
and importance of thé group. 
— 
Structural Characters 
The general structural plan of a Dipnoan is shown in 
the adjoining figure (Fig. 121), taken from a dissection of 
the African form, Protopterus. Its thick, spindle-shaped 
body, enclosed in rounded, horn-like scales, CS, terminates 
in a diphycercal tail, C/ The head is salamander-like 
both in shape and in slimy integument. The paired fins 
(schematized in the figure, P¥, VF) are archipterygial. 
The head region is characterized by a cartilaginous brain 
case, roofed by dermal bones, HR; a mandible, JA, 
directly articulated with the skull (autostylic); an anterior 
and posterior nares, VO,— the former opening under the 
lip, the latter within the mouth ; a row of small, compressed 
(unsegmented) gill arches, GA, whose single outer aperture 
116 
