110 



Derjiopteres.- 



-FISIIES.- 



-PETRfllWYZONTIDS. 



fishes to which they adhere by their mouths. In the 

 MyxiiioiJs, the water of inspiration enters by a single 

 opening on the ventral surface of the boily of the fish, 

 into the pharynx, from whence it passes by six or 

 seven short tubes into an equal number of suborbicular 

 or discoid sacs, to whose walls the gills adhere in form 

 of highly vascular radiated and plaited folds. After 

 having imparted oxygen to the blood circulating in the 

 minute branches of tlie branchial vessels, the water 

 passes out by as many short tubes and openings on 

 each side of the neck as there are gill -sacs (in Bdellos- 

 toma) ; or the short expiratory tubes of one side open 

 into a common canal that leads to an orifice close 

 to the inspiratory one, which is single, and interposes 

 between the expiratory ones, which are a pair, as in 

 the Glutinous hag or Myxlne—iVV^te. 1, fig. 1). The 

 other characters of the group are, a naso-palatine tube 

 or solitary mesial nostril, with a valvular opening in 

 the roof of the mouth ; a feebly organized ej'e ; and 

 a mouth fiu'nished exteriorly with barbels, and armed 

 interiorly by two rows of lingual teeth, with a solitary 

 movable tooth on the palate. In the Myxinoid fishes 

 the spinal column is of firmer structure than that of 

 the lancelet, which has merely a membranous envelope 

 to the myelon. It is an elastic, very flexible gelatinous 

 chord, technically called notochord, composed of a 

 central band of fibres and an exterior sheath, whose 

 dorsal layers separate and form a canal for lodging the 

 myelon ; as do its ventral layers behind the vent, for 

 inclosing the large blood-vessels. No part of this chord 

 is cartilaginous, and the greater part of the skull 

 remains soft, though the acoustic capsules and some 

 other parts of the head are of cartilage. A cartilage 

 also represents the lingual bone, and sustains the lower 

 teeth. None of the Dcrraopteres have a mandible, 

 and they are, moreover, destitute of a distinctly organ- 

 ized upper jaw. Teeth, however, exist on the palate, 

 which resemble indurated mucoid papilhe. There are 

 also some cartilaginous rings in the single mesial nostril 

 tube, whose inner membrane is longitudinally plaited. 

 These fishes are destitute of an arterial bulb or stem, 

 but they have a contr.ictile organ, or portal heart, for 

 expediting through the liver the venous blood coming 

 fmni the viscera of the abdomen. 



THE GLUTINOUS HAG {Myxinc rjl ut iiwsa)—Thte 1, 

 fig. 1 — of the northern seas, is the best known member 

 of the sub-order. Bloch called it Gastcrohranchus 

 ccccus, from the situation of its gill-openings and the 

 minuteness of its lowh'-organized eyes, giving it the 

 appearance of blindness. P.y English fishermen it is 

 frequently named the " Borer," because of its presumed 

 habit of perforating fishes. Sundevall, who studied it 

 in the Norwegian seas, says that it is common in places 

 where cod-fish abound, choosing a clayey or muddy 

 bottom, and avoiding a sandy one ; living habitually 

 in a depth of water varying from thirty feet to seven 

 hundred. AVhen placed in a vessel full of salt water 

 it lies as if dead, or if disturbed swims slowly like an 

 eel ; and if put into fresh water it speedily dies. lie 

 is of opinion that it does not attack living fishes, but 

 enters dead ones by the gill-openings. As many as 

 twenty of these parasites were found in a haddock, 

 which had died when suspended to a hook. They 



had consumed all the flesh to within two or three inches 

 of the gills. When from any cause a series of hooks 

 have not been visited for a week or so, the fishermen 

 on taking them up often finds merely skeletons of fish 

 hanging to them, the Borer having picked the bones 

 clean. On this account the Norse fishermen name 

 the phmderer, Pir-al, or Pil-al (the Picking-eel or 

 Pillager). 



The southern member of the family was discovered 

 in Queen Charlotte's Sound, New Zealand, during 

 Cook's second voyage. Forster says that it is lively 

 and nimble, and that it was often taken adhering to 

 pieces of fish let down into the sea as bait. It shed 

 mucus of a milky hue copiously. The New Zealanders 

 roasted and ate it, notwithstanding its disgusting aspect. 

 There is a third species in the seas of Chili [Bdellos- 

 toma X'olytixma), which has fourteen stigmata on each 

 side. 



Family III.— PETROMYZONTIDS or LAJI- 

 PREYS.— (Plate 1, fig. 2.) 



In this family there are seven stigmata on each side 

 of the neck, each entering a transversely oblong gill- 

 sac, which internally communicates by a small opening 

 with a mesial tube common to all the sacs of both 

 sides, and lying beneath the oesophagus or commence- 

 ment of the digestive canal, but distinct from it. This 

 pharyngeal respiratory tube is closed at its distal end, 

 and anteriorly communicates with the gullet by a 

 valvular opening. When the mouth is free, the water 

 of inspiration enters by it, fills the pharyngeal tube, 

 and then flowing into the gill-sacs, and bathing the 

 fixed gills lining their sides, is finally expelled by the 

 seven stirimata on each side of the neck. When a 

 Lamprey adheres by its suctorial mouth to another 

 fish, or to a stone, access being then denied to the 

 respiratory fluid through the proximal opening of the 

 pharyngeal tube, the water enters the lateral stigmata 

 and is expelled again by them, the current in and out 

 alternating. Professor Owen experimenting on a Lam- 

 prey foinid that when the fish was allowed to fix itself 

 to the side of a vessel, and was held so that the stig- 

 mata of one side only were out of the water, the respira- 

 tory currents were observed to enter by the submerged 

 orifices, and to be discharged with force through the 

 exposed ones. The gill-sacs of the Lampreys are sup- 

 ported by what Miiller has well named a cartilaginous 

 basket, which is wanting in the myxinoids, and yet has 

 an obvious homology with the soft respiratory pharyn- 

 geal barrel of the lancelets. It is a firm but elastic 

 frame-work of cartilage, perforated by numerous wide 

 interstices in addition to the seven on each side for the 

 gill-openings, which are themselves, each encircled by 

 its own detached, cartilaginous ring. The basket is 

 suspended by about seven pairs of cartilages to the fore 

 part of the spinal cord, and occupies most of the dia- 

 meter of tlie fish. Thin cartilaginous plates exist in the 

 fibrous sheath of the spinal cord itself, being an advance 

 in the structure of the neural arches from the mem- 

 branous neural canal of the myxinoids ; a broad, heart- 

 shaped cartilaginous plate of the skull covers the 

 suctorial mouth, and various cartilaginous processes 



