CHONDROPTERYGII. 591 



small aperture, and thus makes its way into the body of Cod, of 

 other fishes which it attacks. (See general account of Fishes.) 



FOURTH ORDER. BRANCHIOSTOMA, (Gr. branchia, gills ; stoma, 



mouth.) 



The term here used to designate an order, is sometimes em- 

 ployed as generic, and the name Amphioxida, (37,) given to the 

 family of which it constitutes the sole genus. Miiller, (see his 

 classification,) ranks it in the sub-order PHARYNGOBRANCHII, 

 (Gr. throat-gills.) a name referring to the position of the branchial 

 sac. This extraordinary animal, at an early period thought to 

 be a mollusk, was first discovered on the British coast, during 

 the latter part of the last century. Muller is no doubt correct 

 in saying, " it is evidently a vertebrated animal and a fish," 

 though it has mare the aspect of a worm than a fish. Yarrel 

 in his "History of British Fishes," calls it the LANCELET, Am- 

 phioxus lanceolatus,, (Plate XIV. fig. 12.) It has a naked skin 

 and no fin except the dorsal, which extends over the entire length 

 of the back. The mouth is entirely inferior, elongated or circu- 

 lar, the margins having a row of filaments. 



The vertebrae are reduced to a single, cartilaginous column 

 or thread, flexible, transparent, and scarcely to be distinguished 

 from the horny pen enveloped in the flesh of some of the Cut- 

 tle-fish. There is no trace of a brain, and the heart " presents 

 entirely the form and distribution of blood vessels and extends 

 over wide spaces," characters of themselves sufficient to distin- 

 guish the Branchiostoma from all other fishes. The blood is 

 white. Muller considers it connected with the Cyclostomatous 

 fishes through its dorsal chord and the absence of jaws ; but as 

 inferior to them in not having a distinct brain and in the pecu- 

 liarities of its respiratory system. The Lancelet is only about 

 two inches in length, and lives in sandy ground at a depth of be- 

 tween ten and twenty fathoms of water. It probably buries 

 itself in the sand. Other curious particulars could be given 

 relating to this lowest of the Vertebrates, did our limits permit, 

 but here we close our account of the Fishes and of the sub-king- 

 dom VERTEBRATES, to which they belong. 



It is difficult to state with accuracy the number of species be- 

 longing respectively to the several families of Fishes, as new 

 researches, made from time to time, vary the assigned numbers. 

 The following tabular view is given, however, as an approxima- 

 tion to a true account : 



