CHAMBERS'S INFORMATION FOR THE PEOPLE. 



female deposits her eggs or spawn, leaving to the 

 male the duty of afterwards fertilising them. The 

 teeth of fishes are chiefly designed to serve as 

 means of seizing prey. They are not only placed 

 on the jaws, but also on the tongue, palate, and 

 other parts of the passage leading to the stomach. 

 The lungs of other vertebrates are represented in 

 fishes by the swimming-bladder, which is of 

 sen-ice in floating the animal. 



ORDER i. The Pharyngobranchii includes only 

 a single genus, the Amphioxus lanceolatus, or 

 Lancelet, which differs remarkably from other 

 fishes. It has neither skull nor brain ; the lower 

 jaw and limbs are absent. The spinal column 

 exists in its embryonal form. The heart is repre- 

 sented by pulsatile swellings upon the great 

 vessels. The mouth is in the form of a longi- 

 tudinal fissure, surrounded by filaments, and leads 

 into a pharynx perforated by clefts, which are 

 ciliated, and perform the function of respiration. 

 This singular little fish, which measures about one 



Lancelet (Ampkioxus tanceolatus) : 



a, mouth, seen from below ; b, general figure ; c, hyoid bone, with 

 filaments attached. 



inch in length, is found burrowing in the sand on 

 the shores of the Mediterranean. The body is 

 lanceolate ; and running along the dorsal surface 

 in the median line is an imperfect crust or fin, 

 which expands at the tail into a lancet-shaped 

 caudal fin. 



ORDER 2. The Marsipobranchit'ha.ve the body 

 cylindrical in form, and destitute of limbs. The 

 skull and spinal column are cartilaginous, and 

 the lower jaw is absent. The mouth is round, and 

 supported by a cartilaginous ring, and adapted 

 for adhering to prey. The skin is soft, with 

 scarcely a vestige of scales. The gills are sac- 

 like, communicating internally with the pharynx, 

 and externally by one or more openings situated 

 on the side of the body near the head. It com- 

 prises the Lampreys (Petromyzon), characterised 

 'by having roundish gill orifices on each side of 

 the neck, and by the possession of a tooth within 

 the cartilaginous ring, with which they tear their 



Common Lamprey (Petromyzon marinus). 



prey. There is a marine species two or three 

 feet long, and other smaller ones which inhabit 



156 



rivers. The Myxine (Hag-fish) is blind, and is 

 found parasitic in the interior of other fish, usually 

 the cod, into which it penetrates by means of its 

 singular curved tooth. In this genus, the nasal 

 sac opens posteriorly into the pharynx. 



ORDER 3. The Teleostei, or 'osseous' fishes 

 have a well-ossified skeleton, and the skull is 

 composed of numerous bones. A lower jaw is 

 present. The gills, which are supported upon 

 bony arches, are tufted and comb-like in shape, 

 and lodged in two branchial chambers, each of 

 which communicates internally with the pharynx, 

 and from which the water passes away by a single 

 aperture (gill-slit), which is covered with a bony 

 operculum. The bulbus arteriosus, which is 

 situated immediately in front of the ventricle, is 

 not contractile, and there is never more than a 

 single row of valves separating it from the 

 ventricle. The fins, when present, are supported 

 by rays. The nasal sacs do not communicate 

 posteriorly with the pharynx. 



Sub-order (A). The Malacopteri have soft or 

 many jointed fins that is, fins which are sup- 

 ported by bones, which split up longitudinally as 

 they diverge from a common point of insertion. 

 Further, these bones are divided transversely into 

 shorter pieces. A swimming-bladder is always 

 present, and communicates with the gullet. This 

 sub-order is divided into two groups : I. Apoda, 

 from which the ventral fins are absent, compris- 

 ing the well-known Muranidce, or Eel tribe. They 

 are all lengthened in form, have the spine very 

 flexible, the skin soft and thick, and the scales 

 almost invisible. Many of them inhabit rivers, 

 while others are marine, as the Conger, which is 

 from four to six feet long, and destitute of both 

 pectoral and ventral fins. The Common Eel 

 (Anguilld) can live for some time out of the 

 water. This is due to the smallness of the gill 

 apertures, which keep the breathing organ moist. 



Electrical Eel (Gymnotus electricus). 



The most remarkable form is the Gymnotus, 

 Electrical Eel. It is a native of the South Ameri- 

 can rivers. It attains the length of five feet, 

 and can communicate a shock powerful enough 

 to stun men and horses. The electrical apparatus 

 is largely supplied with nerves, and extends 

 throughout the greater part of its body. By 

 giving these shocks, the animal is greatly ex- 

 hausted, and requires rest and nourishment 

 before it can renew them. In this genus, the 

 anus is placed in front of the gill openings. The 

 second group namely, the Abdominalia have 



