CYCLOSTOMES, LAMPREYS, AND HAGFISHES. 151 



gills are placed not in simple slits, but in large pouches on 

 the sides of the neck, and these pouches may either open 

 separately to the exterior or by means of a tube which leads 

 to a single opening. The number of gill pouches ranges 

 between six and fourteen on either side. 



The Cyclostomes are subdivided into two groups, accord- 

 ingly as the nostril communicates with the throat or not. 

 As examples of the first, the hagfishes may be cited. These 

 are all marine, and are capable of secreting a large amount 

 of mucus from their bodies, so that a few hagfish in a pail 

 will convert the water into a jelly-like mass. These fishes 

 are parasites, and work their way into various fishes, like 

 the cod, and when once inside they eat up all the flesh 

 and viscera, leaving nothing except the skin and bones. 



The second group is represented by the lampreys. Some 

 of these are marine, others live in fresh water, while many 



FIG. 71. Lamprey (Petromyzon marinus). After Goode. 



of the marine forms ascend streams in spring to lay their 

 eggs. By means of their circular mouths, horny teeth, 

 and sucking tongues, the lampreys attach themselves to 

 fishes, from which they suck the mucus and frequently 

 the blood. In some places the large sea-lampreys are 

 regarded as delicacies, but usually they are not esteemed 

 as food. 



