4 FISH GALLERY. 



adult Appendicular^ {Fritillaria furcata), which is one of the few 

 Tunicates that retain the tail in adult life. 



At the end of the case are shown drawings of ten species of 

 the Lancelet. 



CYCLOSTOMI (Lampreys and Hag-fishes). 



Table- The Cyclostomi, or Lampreys and Hag-fishes, are aquatic 



case zz. Vertebrates not included among the " Fishes " or Pisces because 

 of the absence of a hinged lower jaw. The mouth is adapted 

 for sucking; when open it is round in shape (whence the 

 name Cyclostomi, or " round -mouth "), and it is closed by the 

 approximation of the right and left margins ; the teeth are of a 

 horny material and have a vertical succession. The body is long, 

 without scales in the skin ; the tail-fin is simple, and there are no 

 paired fins and no traces of pectoral and pelvic girdles. The 

 nostril is single; the gills are in pouches, the external and internal 

 openings of which are small. The skeleton is fibro-cartilaginous, 

 and the notochord persists for life. Two divisions of the 

 Cyclostomi are recognised, the Hyperoartia (Lampreys) and the 

 Hyperotreta (Hag-fishes). 



In the Hyperoartia the external nasal aperture is on the upper 

 surface of the head, and from the inner end of the nasal sac there 

 leads back a tube which ends blindly above the pharynx (see 

 dissection 1059). There are no barbels. The eggs are small 

 (see 10G0). Each gill-pouch has its own external aperture. The 

 median fins are relatively larger, and are more subdivided than in 

 the Hyperotreta. Various species of the Lamprey occur in the 

 temperate parts of the northern hemisphere, the commonest being 

 the Lamprey, Petromyzon marinus } 1057, and the Lampern or 

 River Lamprey, Petromyzon fluviatilis, 1058. 

 Lamprey. The word Lamprey comes to us from the Low Latin name 

 lampreda or lampetra, the licker or sucker of rocks, applied to 

 the animal on account of its peculiar habit of adhering by its 

 mouth to stones. The generic name Petromyzon applied by 

 scientists refers also to this habit. The mouth when open (1062) 

 forms a sucking disc, with numerous brown, horny teeth arranged 

 in circular and radiating rows, and with some in the centre 



