434 ZOOLOGY. 



Subclass 3. Teleostei (Bony fishes). ~We now come to a 

 type of fishes which, within very recent geological times as 

 well as during the present period, has become differentiated 

 or broken up into thousands of species, corresponding to 

 the complexity of their physical environment as compared 

 with the simple features of the physical geography of De- 

 vonian and Carboniferous land-masses. Like must of the 

 larger groups of animals, as the Decapod Crustacea, and 

 especially the insects, as well as the mollusks, the bony 

 fishes have attained an astonishing amount of specialization, 

 as if the tree of icthyic life, taking root in the Silurian Age, 

 and sending out but a few branches in later Palaeozoic times, 

 had suddenly, in the Cretaceous and Tertiary Ages, thrown 

 out a multitude of fine branches and twigs intertwining and 

 spreading out in a way most baffling to the systematist. 



The essential, diagnostic characters of the bony fishes, i.e., 

 such as separate them from the Elasmobranchs and Ganoids, 

 are as follows : The skeleton is bony, the vertebrae being sep- 

 arate ; the outer elements of the scapular arch are simple, the 

 inner elements for the most part bony and usually three or 

 two in number ; the pectoral fins are without any bone rep- 

 resenting the humerus, and are connected with the scapular 

 arch by several (generally four) narrow bones (Gill). The 

 optic nerves cross one another. The gills are free, usually 

 four on each side, and with several opercular bones. The 

 heart is without a cone, but with an arterial bulb, and with 

 but two valves at the origin of the aorta. The intestine is 

 destitute of a spiral valve. 



The student should dissect a typical Teleost, such as a 

 fresh-water or sea perch, with the aid of the following ac- 

 count of its anatomy. The drawing and account here given 

 of the anatomy of the sea-perch have been prepared by Dr. 

 C. Sedgwick Minot. The common sea-perch or dinner 

 (Tauivyolalrus adxpersns Gill, Fig. 399) resembles the fresh- 

 water perch very closely in its anatomy, the most note- 

 worthy difference being the absence of the cceca at the 

 pylori c end of the stomach in the marine species; with this 

 exception the following description applies almost equally 

 well to the fresh-water perch, so that this account will be 



