50 BOARD OF AGRICULTURE. 



cartilage like those below, is a little more complicated and their 

 organs more perfect in lorm and adaptation. Tliis sub-class re- 

 ceives the name of " Elasmobranchii," or plated gills, from the 

 fact of their having separate and detached breathing apertures on 

 each side of their necks. 



Passing upwards, we come to the sturgeons, where we find a 

 still greater "advance of developement," and more perfect and 

 complicated organs than in those below them. This class is called 

 Ganoidei, from the enamelled plate-like scales with which its rep- 

 resentatives are covered. 



The next, and fourth step upward brings us among fishes with a 

 perfected bony skeleton — showing a complete vertebrated organi- 

 zation, and their several parts constructed with reference to 

 carrying out higher physiological functions, — in short a perfect 

 iish. This sub-class is called Teleostei, perfected bones ; in refer- 

 ence to the completeness and finish of its bony skeleton. 



Here we have four sub-classes, founded on what appears to be a 

 natural series of orders, each representing difl'erent but connected 

 stages ill the creation of the animals under examination. 



These several sub-classes are further divided into orders, the 

 orders into sub-orders, these again into groups and families, the 

 fiimilies into sub-families, and these into genera, and the genera 

 into species. To elucidate this system so as to make it clear and 

 plain, let us begin at the "top of the heap," and go downwards. 

 Commencing, therefore, with the sub-class Teleostei, or perfected 

 bones, let us examine their several distinctive characteristics more 

 minutely and technically, and we shall find them as follows : using 

 in part, Prof. Gill's description of them. * 



Sub-Class Teleostei, Midler. 



The cndo-skeleton (inside frame) is almost always osseous. The 

 scapular arch is suspended from the skull ; the supra scapula gen- 

 erally connected with the mastoid, and paroccipital bones. The 

 exo-skeleton (outside frame) is generally in the form of cycloid, 

 or ctenoid scales, but sometimes the body is naked, and sometimes 

 covered with bony scales, plates or spines. The optic nerves cross 

 each other in their passage from their respective lobes to the eyes. 



* Catalogue of fishes of the eastern coast of North America from Greenland to 

 Georgia, by Theodore Gill. 



