554 
LOWEST VERTEBRATES. 
aperture being situated above the mouth at the extremity of the head, which is 
furnished with four pairs of barbels. The mouth is devoid of lips, the palate 
is provided with a single median tooth, and there are two comb-like series of 
rasping teeth on the tongue. The gill-apertures, or aperture, are situated at a con¬ 
siderable distance from the head; and each gill-poucli has a separate duct opening 
into the oesophagus. The sides of the abdomen carry a row of mucous sacs, and 
there is no spiral valve to the intestine. The large eggs are invested - in a horny 
envelope, furnished with threads for adhesion. In the true hag-fishes, of which 
the common species (Myxine glutinosa ) is found on the coasts of Europe and 
North America, there is but a single gill-opening on each side of the abdomen, 
leading by means of six ducts to as many gill-pouches. Another species has been 
recorded from the extremity of South America; and the range of the genus also 
includes Japan. In the second genus ( Bdellostoma ), of which there are two species 
from the coasts of the South Pacific, there are six or more gill-openings on each 
side, each communicating by a separate duct with a gill-chamber. All these 
creatures are marine, and are frequently found deeply 
buried in the bodies of fishes, more especially members 
of the cod family, into which they bore for the purpose 
of feeding on the flesh. They are totally blind, and 
secrete vast quantities of slime, which seriously inter¬ 
feres with fishing in localities where these creatures 
abound. Met with in the fjords of Norway at a depth 
of about 70 fathoms, hag-fishes have been dredged from 
depths of nearly 350 fathoms. 
Primeval The Old Red Sandstone of Caithness 
Lampreys. has yielded the skeletons of a small limb¬ 
less creature ( Palceospondylus ), which there is little 
doubt must be regarded as one of the forerunners of 
the modern lampreys. Measuring only about a couple 
of inches in length, these skeletons show a well-calcified 
skull, while the notochord is surrounded by a series of 
calcified rings, and the tail has a large fin, of which the 
supports on the upper side are forked like those of 
lampreys. The front of the head has a circular opening 
surrounded with a ring of tentacles ( dc , Ic), probably 
corresponding to the nose of a modern lamprey; the 
opening of the nose itself ( n ) appears to be single; and 
there are a pair of plates ( x ) behind the head not 
improbably representing gill - plates. It may be confidently assumed that this 
little creature is but one among a series of lost types. 
SLIGHTLY ENLARGED RESTORATION 
OP THE SKELETON OP THE 
PRIMEVAL LAMPREY. — After 
Traquair. 
