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-pouch 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 w r hich 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. h as 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 OF THE 

 PRIMEVAL LAMPREY. After 



Traquair. 



