LAMPREYS. 
1181 
lateral line, which still serves one of the most impor- 
tant. senses possessed by fishes and batrachians. 
The lateral-line system of the Lampreys retains 
perhaps a relic, at least a reminder, of the primitive 
condition assumed by Beard, a pore of the system being 
present above each gill-opening (fig. 349, Ibrs). In its 
extension over the body this system is otherwise not 
unlike that of the Teleosts. Behind the eyes run two 
transverse series of pores ( c and stp ) ; and the lateral 
line proper is double (bn and Id). The frontorostral 
branches and their subdivisions are most distinct below 
and before (so) the eyes and in two parallel longitudinal 
rows O') on the upper surface of the snout. Round the 
lower jaw runs a mandibular branch (m), which sends 
out backwards on each side a sub-branchial series (Ibri) 
below the gill-openings. In most cases, however, all 
these pores, except the rostral, are very difficult of 
detection. 
Another primitive condition is manifested, accord- 
ing to Langerhans, in the skin of the Lampreys, its 
outer epidermal layer (cuticular cells) being frequently 
furnished, though irregularly and in patches, with cilia 
— calling to mind a very common appearance in the 
skin of the invertebrates. But in the Lampreys, according 
to Langerhans, these cilia are dead, motionless (sensory 
hairs). Neither the Lampreys nor the following fishes 
show any sign of squamous growths in the skin. 
The intestinal canal of the Lampreys is simple and 
straight, the divisions being scarcely distinguishable from 
without. Only at the extreme front and back is it attached 
by a mesentery to the dorsal wall of the abdominal 
cavity; throughout the rest of its course it lies free in 
the cavity. The anterior part, answering to an oeso- 
phagus and a stomach, is wider but has thinner walls 
than the duodenum, which is lined with longitudinal 
folds, one of them deeper than the rest and bending at 
the middle of ' the duodenum into three or more spiral 
coils. Behind the duodenum and separated therefrom 
by an annular valve, lies a short but somewhat dilated 
rectum. The liver lies as usual in the extreme front 
of the abdominal cavity, and is rather small, but firm 
and without lobes. There is no gall-bladder. The air- 
bladder is also wanting. The kidneys are paired and 
ribbon-like, with the sharp inferior margin hanging free 
in the posterior part of the abdominal cavity, but ex- 
tending forward beyond the middle of its length. Their 
efferent ducts have a common opening at the top of a 
papilla projecting behind the cloaca! aperture and longer 
and more pointed in the males than in the females. 
This common outlet, however, has on each side (to the 
right and left) an opening (a slit) from the abdominal 
cavity, and by this route the sexual products, both ova 
and sperma, after being shed into the said cavity, are 
expelled through the papillar orifice. Both the ovaries 
and the testes are unpaired, suspended between the kid- 
neys, without special deferent canals. When ripe, they 
fill the abdominal cavity throughout its length, sur- 
rounding the shrunken intestine. 
Especially interesting is the foremost part of the 
intestinal canal, the oesophagus, as it appears during the 
metamorphosis of the Lampreys. In their larvae, the 
Prides (Ammocoetes), the branchial cavity (fig. 351, 
br I — 177) communicates directly on the one hand 
(anteriorly) with the pharynx and mouth, on the other 
(behind) with the oesophagus ( oes ) and the intestine, so 
that all food must pass through the branchial cavity in 
company with the water used for respiration. During 
Fig. 351. Section through the forepart of a Pride ( Ammocoetes ), 
about 3 times the nat. size. 
abr, branchial artery, with seven openings, for the arterial branches 
supplied one to each gill-opening; br I — VII , first-seventh branchial 
sacs; C, heart; Oh, notochord; Fly, nostril; La , anterior lip; Lp, 
posterior lip; M, posterior (inner) mouth cavity; Ml, myelon; MT, 
mouth tentacles; oes, oesophagus (anterior part of intestine). 
the metamorphosis, however, the posterior passage is 
closed, and a new oesophagus (fig. 350, oes) is formed 
above the branchial cavity, in the form of a string first 
solid and afterwards hollow. The food receives a special 
passage. The water used for respiration passes neither 
through the mouth nor the nose, but must be received 
and expelled through the branchial apertures. At the 
same time the rostral region is developed, from the 
cornua trabecular urn (see above) to the jaws and denti- 
tion inclusive. 
The family of the Lampreys hardly contains a 
score of species, though more have been described. 
These are distributed among four or five genera, only 
one of which belongs to the Scandinavian fauna. 
