THE LABIPREYS. 223 



(197.) The Petromyzonidce, or lampreys, for the 

 reasons already assigned, we have placed as the most 

 aberrant family in the order. Their very low state of 

 organisation renders them the most imperfect of all 

 vertebrated animals, or, at least, of the whole class of 

 fishes. Their skeleton is so soft as not even to be car- 

 tilaginous : the vertebrae are indistinct, and are per- 

 forated by a central tendinous cord, filled with a muci- 

 laginous substance ; the vertebral column thus becomes 

 a series of rings, and is hardly more solid than the mu- 

 cilage within. The gills, instead of being pectinated, 

 as Cuvier remarks, more resemble pouches, resulting 

 from the union of one of the faces of one gill with the 

 opposite face of the neighbouring gill. In some there 

 are seven branchial spiracles on each side, but in others 

 only one. Their external form, however, is quite suf- 

 ficient to make them immediately known. The body 

 is e€l- shaped, devoid of ventral and pectoral fins, or, in- 

 deed, of any true fin ; for that elongation of the skin 

 which forms the dorsal and unites to the ventral is devoid 

 of any rays : the mouth is circular, placed on the lower 

 part of the head, and forms a maxillary ring. Such 

 as have the mouth armed with rows of strong teeth and 

 tubercles, Hke the true lampreys, are able, by this ap- 

 paratus, to adhere to stones and other substances with 

 astonishing tenacity ; by the same means they are said 

 to attack the largest fishes, which they pierce and devour 

 by their rasp-like teeth. Of this very remarkable family, 

 three principal types, or genera, are only known : the 

 first is Petromyzon, or the true lampreys, having several 

 lateral spiracles ; the second is Myxene *, where the 

 spiracles are only two ; the third is represented by the 

 AmpJiioxus of Mr. Yarrell : the whole may be charac- 

 terised by having the skeleton almost mucilaginous ; the 



* Subsequently named Gastrobranchus by Bloch, who has admirably 

 illustrated its internal structure. This group, as seen in the Bdg?ie Anwia'i, 

 is another instance of the Linnasan genus Myxene being nominally retained, 

 but virtualiy abolished : Cuvier divides Myxene into three genera, but does 

 not retain the original name to any one. The nomenclature and the 

 arrangement appear to us equally objectionable. 



