692 



FISHES. 



sacs and apertures on each side behind the head; the inner 

 branchial ducts terminate in a separate common tube. Intestine 

 with a spiral valve. Eggs small. The larvce without teeth, 

 and with a single continuous vertical fin. 



" Lampreys " are fotind in the rivers and on the coasts of 

 the temperate regions of the northern and southern hemi- 

 spheres. Their habits are but incompletely known, but so 

 much is certain that at least some of them ascend rivers 

 periodically for the purpose of spawning, and that the young 

 pass several years in rivers, whilst they undergo a metamor- 

 phcsis (see p. 170). They feed on other fishes, to which they 

 suck themselves fast, scraping off the flesh with their teeth. 

 Whilst thus engaged they are carried about by their victim ; 

 Salmon have been captured in the middle course of the 

 Ehiae with the Marine Lamprey attached to them. 



Fig. 315. — Mouth of Larva of Fig. 316. — Mouth of Petromyzon fluviatilis^ 



Petromyzon branchialis. mx, Maxillary tooth ; md, Mandihulary 



tooth ; I, Lingual tooth ; s, Suctorial teethe 



Petromyzon. — Dorsal fins two, the posterior continuous with 

 the caudal. The maxillary dentition consists of two teeth placed 

 close together, or of a transverse bicuspid ridge ; lingual teeth 

 serrated. 



The Lampreys belonging to this genus are found in the 

 northern hemisphere only ; the British species are the Sea- 

 Lamprey (P. marinus), exceeding a length of three feet, and 

 not uncommon on the European and North American coasts ; 

 the Eiver-Lamprey or Lampern {P. fluviatilis), ascending in 



