334 PISCES. 



appearance of sacs produced by the union of the faces of the proximate ones. The labyrinth of the ear 

 is embedded in the cranium, and the nostrils opened by a single orifice, in front of which is a blind 

 cavity, improperly thought a spiracle. The intestine is straight and slender, with a spiral valve. 



Pctromyzon, the Lampreys, have seven gill-openings on each side, and the skin on the upper and under parts of 

 the tail is formed into fin-like crests, which, however, have no rays. The Lampreys properly so called, have strong 

 teeth in the maxillary ring, and the inner disc of the lip, which is very circular, is covered with tubercles, hard and 

 crusted like teeth : this ring is suspended by a transverse plate answering to the intermaxillaries, and there are 

 vestiges of maxillaries on the sides. The tongue, which moves backwards and forwards like a piston, and performs 

 the suction, has two longitudinal rows of small teeth. Water reaches the gills- from the mouth by a particular 

 membranous canal, a sort of trachea, placed under the gullet and perforated with holes ; there is a dorsal before 

 the vent, and another behind it which unites with the caudal. They habitually fix themselves to stones and other 

 hard substances by means of the sucker ; and they attach themselves to the largest fishes in the same manner, and 

 in the end pierce their integuments and prey upon their substance. 



The species are — P. marinus, the Sea Lamprey, two or three feet long, marbled with brown and a yellow ground; 

 the first dorsal separate from the second ; two large teeth on the upper part of the maxillary range. In spring they 

 approach the mouth of rivers, and their flesh is highly esteemed. P. fluviabilis, the River Lamprey, from a foot to 

 eighteen inches long ; silvery, with blackish or olive spots on the back ; two large teeth in the maxillary ring; found 

 in the fresh waters. P. planerii, the Small River Lamprey, is eight or ten inches long, and has the colours and 

 teeth of the preceding : it also inhabits the fresh waters. [The last two are often styled Lamperns.] 



Myxine.—Th& members of this genus have but one tooth in the maxillary ring, which is entirely membranous ; 

 two rows of strong teeth on each side of the tongue ; but in other respects like the Lampreys. The mouth is 

 circular, with eight cirri, and has a spiracle on the upper margin which reaches the interior. The body is cylin- 

 drical, and furnished with one fin round the extremity of the tail. The intestine is straight, but simple, and plaited 

 internally, and the liver has two lobes : no eyes are perceptible. Their eggs grow to a large size ; they discharge 

 60 much mucus from the pores in their lateral line that if kept in a vessel of water they turn it into a jelly ; they 

 attack fishes in the same manner as the Lampreys, and they are divided into subgenera according to the number 

 of their gill-openings. 



Heptratremus, has seven on each side, like the Lampreys, and the only known species is from the South Sea. 



Gastrobanchtis, has a common canal to the gills on each side, each of which opens by a hole near the heart, and 

 at one third of the length from the head. G. glutinosa, the Hag, is the only known species, and it enters the mouths 

 of fishes when on the fishermen's line, and plunders their substance. 



Ammocetes, has the entire skeleton so soft and membranous that there is not a bone in the whole, not even a 

 tooth ; they have the external form and gill-openings of the Lampreys, but their fleshy lip forms only a semicircle 

 on the upper part of the mouth, which is furnished with numerous cirri. The known species, A. branchialis, is 

 from six to eight inches long, about the thickness of a goose-quill, and of no use but as bait for other fish. [It has 

 been accused of sucking the gills of other fishes, but perhaps falsely. It is found in the sand and mud of small 

 streams ; preys on worms, insects, and dead matter, and is, in return, preyed on by the Eel.] 



lAmphioxus, has the body compressed, the surface without scales, and both ends pointed. It has a dorsal along 

 the whole line of the back, but no other fins. The mouth is on the under side of the body, opens longitudi- 

 nally, and has a row of filaments on each side. A. lanceolatus, the Lancelet, is the only known species. It is a 

 British fish, and an inhabitant of the sea, in which it is found, although very rarely, lurking under stones in 

 pools left by the ebbing tide. Pallas considered it as a molluscous animal, and not a fish ; but Mr. Yarrell, in his 

 British Fishes, argues that it is a fish, and that in organization it is the lowest of the class. " The form of the 

 fish," says Mr. Yarrell, " is compressed ; the head pointed, without any trace of eyes ; the nose rather produced ; 

 the mouth on the under edge, in the shape of an elongated fissure, the sides of which are flexible ; from the inner 

 margin extend various slender filaments, which cross and intermingle with those on the opposite side. Along 

 the sides of the body the muscles are arranged in regular order, diverging from a central line; one series passing 

 obliquely upward and backward, and the other srt'ies as obliquely downward and backvard ; the anal apertuie is 

 situated one-fourth of the length of the fish in advance of the end of the tail ; the tail itself pointed ; from the nose 

 to the end of the tail, a deUcate membranous dorsal fin extends the whole length of tlw back, supported by very 

 numerous and minute soft rays; the surface of the body smooth." These charactei s leave no doubt that the 

 animal is a fish ; but that it ought to be classed with the Lamprey family is another matter. The specimen from 

 which the description was made was not above an inch in length, very slender, and aim ist transparent.] 



