146 NATURAL HISTORY. 



duct is not lined with cartilaginous rings in the manner of trachea. This duct opens by valvular 

 apertures on the roof of the mouth. Sir Richard Owen, however, regards this organ rather as 

 representing the spiracles of Sharks, which run from the top of the head to the sides of the 

 branchial chamber. There are barbels on the head, the mouth has no lips, there is one tooth on the 

 palate, and two teeth like small combs on the tongue. The branchial apertures are far removed from 

 the head ; mucous sacs extend all along each side of the abdomen. The intestine in these fishes, 

 unlike that of the Lampreys, has no spiral valve. The eggs, too, are relatively large, and are con- 

 tained in horny cases provided with short filaments, by which they become attached. 



THE HAG.* 



The vertebral column in this fish consists of soft substance, showing scarcely any trace of division 

 into vertebral rings, the cartilage surrounding the semi-fluid primitive notochord. The usual 

 length is about a foot ; the body is compressed behind ; the snout is conical, but rather blunt ; the 

 caudal fin. reaches forward to the vent \ its rays are numerous. There is another fin between the vent 

 and the gill-openings which contains short stout rays. The lateral line contains more than a hundred 

 glands, which form a bead-like chain along the body, and from these the mucus is poured out, which 

 has suggested the specific name of the fish. Water enters by the nasal tube, so as to supply the gills ; 

 and in this respect cyclostomous fishes form an exception to the general law that the nostril has no 

 respiratory function in fishes. The only other fishes in which the nostril opens on the palate are the 

 Dipnoi, t At the back of the gullet in the Hag are six small tubes communicating with the sacs which 

 replace the ordinary gills of fishes, and from these gills are passages which unite on each side 

 into a single tube, opening on the belly, at about a third of the length of the animal from its mouth. 

 The portal vein in this fish has a rhythmic contraction. The quantity of slime secreted from the 

 body is prodigious. Couch mentions that a single individual placed in three or four cubic feet of 

 water filled it so completely with the mucous secretion that the entire mass could be lifted out with a 

 stick in a continuous sheet ; and hence some of the older naturalists believed this fish had the power 

 of converting water into glue. The eggs are large and yellow ; no more than twelve Lave been found 

 at one time in a developed state in the ovary. The ovary is placed below the notochord, and consists 

 of 'plates. The fish is remarkably sluggish, but when it moves swims like an Eel. It frequents muddy 

 ground, and lives in deep water. It is rarely captured, and never approaches the shore. It extends 

 along the coasts of Europe and North America, but is chiefly known from northern waters. The mode 

 in which this animal feeds is one of the most singular facts of natural history, since it enters by the 

 natural apertures into the bodies of Mackerel and various fishes of the Cod family, and devours not 

 only the intestines but often the flesh also. Sometimes the fisherman draws up on his line a Haddock, 

 of which nothing remains but the bones and skin. This destruction is sometimes accomplished by a 

 single Hag, but as many a,s twenty have been found in the body of a single fish. The Hag has 

 occasionally been found partly digested in the stomach of a Cod. Another species is found in the 

 temperate parts of the Pacific coast of South America. 



The genus Bdellostoma, with a general resemblance to the Hag, has many branchial apertures on 

 the sides of the body, each of which leads by a separate duct to a gill or branchial sac. 



In the Bdellostoma cirratum, found at the Cape of Good Hope and New Zealand, there are six 

 or seven of these gill-openings on each side, but in the Bdellostoma polytrema, from the coast of Chili, 

 there are fourteen, openings for the gills extending along each side of the abdomen. Thus in external 

 appearance this fish presents some resemblance to the yet lower Amphioxus, which is the last and 

 most degraded member of the fish class that is known. 



* Myxine glutinosn. 



t The following sentence was omitted from the account of the Mud-fish on p. 20, and should be added to the paragraph 

 containing a statement of Sir Richard Owen's opinion : " Subsequent researches, especially those of Professor Huxley, have 

 demonstrated that the nasal sacs of Lepidosiren open on the inside of the upper lip, so as to form true posterior nares ; but 

 this correction does not affect the general truths of Owen's generalisation as to the closed nasal sac being a distinctive 

 character of fishes." 



