192 LAMPREYS. 



by the external openings of the gill-sacs. " If a Lamprey, while so attached to the side of a 

 vessel, be held with one series of apertures out of the water, the respiratory currents are seen 

 to enter by the submerged orifices, and after traversing the corresponding sacs and the pharynx, 

 to pass through the opposite branchiae, and to be forcibly ejected therefrom by the exposed 

 orifices The cyclostomous fishes thus present an obvious affinity to the Ccphalapoda, inas- 

 much as the branchial currents are independent of the parts concerned in deglutition." — 

 (Prof. Owen, Catal. P/iys. Scr. Jlliis. R.C.S., ii. p. 80.) The heart has an auricle and a 

 ventricle, but no bulbus arteriosus. The alimentary canal is straight, simple, and without 

 csecal appendages; there is no s\vim-b!adder. Probably all the species go through a meta- 

 morphosis. 



The Pctroniyzoufida are found in the fresh waters and around the sea-coasts of the 

 temperate regions of both hemispheres. By means of their suctorial mouths they attach 

 themselves to other fishes, and scrape off their flesh by their rasp-like teeth. The food con- 

 sists also of worms and insect larva?. The British species are three In number, and are all 

 of them excellent food ; but owing to the small size of one of the species, only two are of 

 any commercial value. 



