CHAPTER l8 



THE PINEAL SYSTEM OF THE CLASS PISCES 



This class includes the cartilaginous and bony fishes, the Holocephali 

 and Dipnoi. Besides the living representatives of the class, there are 

 many extinct forms (for example, Fig. 140) the consideration of which is of 

 the greatest importance with respect to the history and nature of the 

 pineal system as a whole. 



The study of the pineal organs in the various types of living fishes 



Fig. 140. — Dorsal View of the Head of Dipnorhynchus, a Primitive Fossil 

 Fish from the Middle Devonian Rocks of New South Wales. (Reduced 



b) 

 A median spine subdivides the anterior border of the parietal foramen, there being 

 a crescentic notch on each side of it. This is considered to be an indication 

 of the bilateral origin of the parietal organ. 



P.F. : parietal foramen. FR. : frontal. 



PAR. : parietal. N. : nasal. 



/. PAR. : interparietal. TAB. : tabular. 



(After E. S. Hills.) 



at first sight appears as if it would be somewhat barren. There is no 

 well differentiated sense-organ such as that in Cyclostomes and certain 

 reptiles ; nor is there any special development of the proximal part, as 



