IX. — FISHES. 69 



sand or mud on the approach of drought, and are able to survive 

 thus for many months, when rain comes they emerge in wreat 

 numbers, which accounts for the so-called "showers" of fishes 

 frequently reported in the newspapers, (4.) the Queensland 

 " Mud-hopper" or " Climbing Fish" {Perio]jhthalmus) which leaves 

 the water, progressing in advance of the flowing tide by a series 

 of leaps, and even ascends the mangrove trees ; many other 

 instances might be adduced but the above are sufficient for our 

 purpose. 



Fishes, although living almost entirely under water, breathe 

 oxygen, which they obtain from the water by means of their 

 gills ; and although nearly all fishes are oviparous, some hatch 

 out the eggs inside the body (Cristtceps, Mustelus, &c.) ; others 

 in a sub-caudal pouch (Syngnaihus, &c.) ; others again in the 

 mouth of the male parent (Hemipimelodus, &c.) 



Fishes are the oldest recognised types of vertebrate animals, 

 remains having been found in the Upper Silurian strata, near 

 Ludlow. They are classified as on pages 16 and 17. 



The first sub-class, the PAL^IOHTHYES, has been sub- 

 divided into two orders (i.) the Chondropterygii, including 

 Sharks, Rays, and Chimseras, and (ii.) the Ganoidei, which latter 

 are but little represented in recent times though at one time 

 they existed in large numbers. 



Order OHONDROPTERYGYII. The principal families 

 of this order are (1) the Carchariidm, to which belong such 

 formidable creatures as the Blue Shark {Owrcharias glaums), 

 the Whaler (C. macrurus), the Tiger Shark (^Galeocerdo ratjneri), 

 and the Hammer-head [Si^hyrna zygcEna), with many smaller 

 forms ; (2) the Lamnidce, containing the no less formidable Blue 

 and White Pointers {Lamna glauca and Carcharodon rondeUiii), the 

 Grey Nurse {Odontaspis taunts), the curious Fox Shark or Thresher 

 (Alopias vulpes), and the still more curious Basking Shark 

 {Getorhinus m^'ajmws), which grows to over thirty feet in length, 

 but is quite harmless ; (3) the Heterodontidod, to which belong 

 the Port Jackson or Bull-head Sharks [Heterodontus phillipi and 

 E. galeattis), stud which is interesting on account of its great 



F 



