Dermoptbbes. FISHES. Petromyzontids. 
110 
fishes to which they adhere by their mouths. In the 
Myxinoids, the water of inspiration enters by a single 
opening on the ventral surface of the body 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 oxj'gen to the blood circulating in the 
minute branches of the 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 Myxine — (Plate 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 eye ; and 
a mouth furnished 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 laucelet, 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 
I’emains soft, though the acoustic capsules and some 
other parts of the head are of cartilage. A cartilage 
also represents the lingual hone, and sustains the lower 
teeth. None of the Dermopteres have a mandible, 
and thej- are, moreover, destitute of a distinctly organ- 
ized upper jaw. Teeth, however, exist on the palate, 
which resemble indurated mucoid papillae. 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 contractile organ, or portal heart, for 
expediting through the liver the venous blood coming 
from the viscera of the abdomen. 
THE GLUTINOUS HAG {Myxine glutinosa) — Plate 1, 
fig. 1 — of the northern seas, is the best known member 
of the sub-order. Bloch called it G aster ohranchus 
cozens, from the situation of its gill-openings and the 
minuteness of its lowly-organized eyes, giving it the 
appearance of blindness. By English fishermen it is 
frequently named the “ Borei',” 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. When 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 bj'' 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 plunderer, 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 polytrema), which has fourteen stigmata on each 
side. 
Family III.—PETROMYZONTIDS or LAM- 
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 
wnth 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. A¥hen 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 stigmata 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 found that when the fish w'as 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 Muller has well named a cartilaginous 
basket, which is w’anting in the myxinoids, and yet has 
an obvious homology with the soft respiratory pharyn- 
geal barrel of the laneelets. 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 the 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 
