GS GUIDE TO THE AUSTRALIAN MUSEUM. 



IX. 



FISHES. 



'i'liESE are the lowest recognized forms of vertebrated animals. 

 The earliest known — and now for the greater part extinct — forms 

 liad a cartilagenous skeleton, that is to say the bones, even in the 

 adult state, were represented by a substance resembling "gristle," 

 but many of the later, and sometimes extinct groups, dating back 

 as far as the cretaceous period, are true Teleosteans, which implies 

 that they possess a bony skeleton and completely formed vertebrae, 

 and to this highly specialized sub-class the greater number of recent 

 fislies belong ; they are cold-blooded animals, destitute of lungs, 

 which are replaced by gills, a character whose permanency 

 constitutes the chief difference between this and the preceding 

 class. Most fishes are oviparous, but a few genera are ovo- 

 viviparous. The majority of the genera are provided with a 

 scaly covering to the epidermis, as in Perca, but in some the 

 skin is absolutely naked, as in Conger^ while a few of the 

 older forms are protected by bon}" scutes, as in the Ganoids, and 

 some recent genera have a hard continuous carapace, as shewn in 

 Ostracion and Aracana. They are almost always wholly aquatic, 

 a few species only being able to exist for a time under other 

 conditions ; that certain genera can sustain life out of their natural 

 element has, however, been long known ; for example we may 

 mention, (1.) the "Climbing Perch" Anahas, of India, which 

 is not only able to leave the water, but by means of its strongly 

 denticulated opercles has been known to climb the sloping 

 sides of trees to a height of several feet, presumably for the 

 purpose of feeding on the insects concealed in the crevices 

 of th(i bark ; (2.) the Eel {AnguiUa) which migrates over 

 land from place to place in search of water, and has also been 

 proved to make nightly excursions over the meadows adjoining 

 its haunts; (3.) many fishes in tropical climates where the supply 

 of water is precarious, are accustomed to bury themselves in 



