1190 
SCANDINAVIAN FISHES. 
dm.“ long. What are the causes that retard the meta- 
morphosis or accelerate the growth of the larvae, we 
do not know; and sometimes we find in the same Ava- 
ters Prides which are larger than the Lamperns*. 
The size, the teeth, the closer proximity of the 
fins, and the usually immaculate colour distinguish the 
Lampern from the preceding species; “but in all other 
relations of form, both external and internal”, Avrote 
Lacepede, “the Iavo Lamprey species are so like one 
another that they seem to be two copies of the same 
model”. The Eel-like body is here too more or less 
terete in front, laterally compressed behind, Avith the 
same variability as in the Sea Lamprey, though some- 
Avhat greater 0 . 
O 
The length of the head to the first gill-opening 
varies in the true Lamperns between about 14 and a 
little over 10 % d of the length of the body, the per- 
centage being least in the oldest specimens; but here 
too it is as a rule greater than the length of the series 
of gill-openings 0 . In the Prides, on the other hand, 
the length of the head is only about 6 7 2 — 7 1 / 2 % of 
that of the body and ahvays less than that of the 
branchial region, which occupies about 12- — 1 2 * 1 / 2 % of 
the last-mentioned length. The length of the snout to 
the anterior margin of the eyes is in the Lamperns 
about V 3 (60 — 68- r %), in the Prides only 1 / 2 , of the 
length of the head. These differences are external ex- 
pressions of the alterations involved by the metamor- 
phosis; but hereAvith too is connected the great differ- 
ence in the structure and form of the mouth and oral 
disk. The Prides (PL LIII, figs. 3 and 4) are toothless 
and never attach themselves by suction. They lead a 
more worm-like life, buried in sand or mud. Their 
mouth is edged in front and on the sides Avith a horse - 
shoe-shaped or semiquadratic anterior lip (fig. 351, 
La), the lateral parts of Avhich are rounded and pen- 
dent, passing evenly or with a shalloAV sinus into the 
corners of the anterior side, but sharply terminated be- 
hind, Avhere they enclose betAveen them the shallower, 
transversal posterior lip ( Lp ). The outer mouth cavity 
is forniciform, Avith a patch of small papilke, set in rows, 
at the middle of the roof, and is bounded behind by a 
coroniform series of concentrically directed processes Avith 
verrucose ramifications (papillae, MT). Behind this co- 
rona lies an anterior pharyngeal cavity (inner buccal 
cavity M), of somewhat smaller capacity than the other 
and bounded behind by an annular, contractile valve 
(velum, vet), Avhose lateral parts are tumid; and behind 
this again lies the still smaller true pharynx, the en- 
trance to the tubiform branchial cavity, through which 
the food too must pass. In the anterior pharyngeal 
cavity the lingual apparatus is developed. The corona 
of papilla? disappears. The lips are thickened, but 
coalesce into a ring, Avhich becomes the suctorial disk 
of the Lampern (PI. LIII, tig. 2). The most important 
differences betAveen the suctorial disks of this species and 
the preceding one have been already noticed. Here the 
disk is both smaller — the dimensions of the snout being 
thus also reduced — and more feebly armed. The edge 
is fringed Avith papillae here too, but sometimes only in 
a single toav. Just Avithin the margin we see a ring of 
small horny teeth ( est ), like the other teeth pointed or 
blunt, Avhite or yellow* 7 . Within the anterior part of 
this ring and parallel to it, Ave find in ordinary cases 
a curved row of similar, simple teeth ( 1st ), and the rule 
is that the remaining surface of the suctorial disk, out- 
side the composite teeth of the mouth, is smooth or very 
finely verruculose. This is one of the most patent char- 
acters of the species, in contradistinction to the lozenged 
comparting of the suctorial disk in the Sea Lamprey, 
Avhere the gums round the bases of the several suctorial 
teeth are bounded by grooves intersecting in a diamond 
pattern (see fig. 352). Frequently, hoAvever, Ave find 
here too, in the Lampern, scattered suctorial teeth on 
the anterior part of the disk, and in a pair (c? and 9) 
of Lamperns from Archangel (fig. 353), Avhich are other- 
Avise quite typical specimens — only that the middle pair 
of the lateral teeth of the mouth, a peculiarity Avhich is 
a 2 dm., according to Benecke. 
6 At Helgevarma Mill, near WexiS, Baron G-. C. CederstrSm caught, in May, 1857 and 1860, Prides 145 mm. long and Lamperns 
(forma Planeri ) 120 mm. in length. 
0 The greatest depth of the body varies in the Lamperns from about 7^2 to nearly 9 % of the length thereof. In the small Prides, 
which as a rule, however, have a more tumid branchial region, the depth behind this is sometimes only 6'/ 3 % of the length of the body. 
d 10'3 is the least percentage we have found for this relation. 
e An exception is adduced by Kroyer in the largest Lampern measured by him. The variations may be due, however, to the dif- 
ferent degree of contraction in the snout and dorsal muscles at death or in alcohol. 
f In the preceding species 68 — 75 %. 
S' The dental differences in these respects are so variable that we have not been able to reduce them to any rule ; but it would appear that speci- 
mens from the sea or with only intumescent genital organs and not yet shrunken intestinal canal most often have the most pointed and whitest teeth. 
