1190 



SCANDINAVIAN FI.SHKS. 



dm." long. What are tlic causes tiiat retard the iiieta- 

 morpliosis or accelerate the growth of the larvtc, we 

 do not know; and sometimes we tind in tlie same wa- 

 ters Pi'ides wiiicli are larger tlian tlie Lamperns''. 



The size, the teeth, the closer proximity of the 

 tins, and the usually immaculate colour distinguisli the 

 Lam])ern from the preceding species; "hut in all other 

 relations of form, both external and internal", wrote 

 Lacepede, "the two Lamprey species are so like one 

 another that they seem to he two cojiies of the same 

 model". The Eel-like body is here too more or less 

 terete in front, laterally compressed behind, with the 

 same varial)ility as in tlie Sea Lamprey, though some- 

 what greater'. 



The length of the head to the tirst gill-o])ening 

 vai'ies in tlie true Lamperns between about 14 and a 

 little (jvei- 10 %'' 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'. In the Prides, on the other hand, 

 the length of the head is only about ^^1., — T^l., % of 

 that of the body and always less than tiiat of the 

 branchial region, which occupies about 12 — li'/j % of 

 the last-mentioned length. The length of the snout to 

 the anterior margin of the eyes is in the Lamperns 

 about '/3 (60—68' %), in the Prides only Vs, of the 

 length of the head. These dift'erences are external ex- 

 pressions of the alterations involved by tlie metamor- 

 phosis; but herewith too is connected tlie great differ- 

 ence in the structure and form of the mouth and oral 

 disk. The Prides (PI. LIII, figs. 3 and 4) are to.ithless 

 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 with a horse 

 shoe-shaped or semiquadratic anterior lip (fig. 351, 

 l/i), the lateral parts of which are rounded and pen- 

 dent, passing evenly or with a shallo^\• sinus into the 

 corners of the anterior side, but sliarply terminated lie- 

 Iiind, where they enclose between them the siiallower. 



transversal ])osterior li|) (7.^)). The outer mouth ca\ity 

 is forniciform, with a patch of small pajiilla?, set in rows, 

 at the middle of the roof, and is bounded behind by a 

 coroniforin series of concentrically directed processes with 

 verrucose ramifications (papilhe, 3/T). Behind this co- 

 rona lies an anterior pharyngeal cavity (inner buccal 

 cavity 71/), of somewhat smaller capacity than the other 

 and bounded behind liy an annular, contractile valve 

 (velum, re?), whose lateral parts are tumid ; and l)ehind 

 this again lies tlie still smaller true pharynx, the en- 

 trance to the tubiform branchial cavit}-, through wdiich 

 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, which becomes the suctorial disk 

 of the Larapern (PL LIII, tig. 2). The most important 

 differences between 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 with papillie here too, but sometimes only in 

 a single row. Just within the margin we see a ring of 

 small horny teeth (e-s/), like the other teeth pointed or 

 blunt, white or yellow'. Within the anterior part of 

 this ring and parallel to it, we tind in ordinary cases 

 a curved row of similar, simple teeth (is^, and the rule 

 is that the remaining surface of the suctorial disk, out- 

 side the com]iosite 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 lozengedP 

 comparting of the suctorial disk in the Sea Lamprey, 

 where the gums round the bases of the several suctorial 

 teeth are liounded by grooves intersecting in a diamond 

 pattern (see fig. 352). Fretpiently, however, we find 

 here too, in the Lampern, scattered suctorial teeth on 

 the a.nterior i),-irt of the disk, and in a pair (cf and 9) 

 of Lamperns from Archangel (tig. 3.')3), which are other- 

 wise (|uite ty|)ical specimens — only tliat the middle pair 

 oi the lateral teeth of the mouth, a pt'culiarit\' which is 



" 2 dm., according ty Bkneoke. 



'' At Helgevarma Mill, near Wexiii, Baron (J. C. CedeusthOm caught, in May, 1857 and ISfiO, Prides 145 nnii. long and Lamperns 

 (forma Planeri) 120 mm. in length. 



' Tlie greatest depth of the body varies in the Lamperns from abont 7'., to n(.'arly 9 % of (lie length tliereot. In the small Prides, 

 wliicli as a nde, however, have a more lunnd branchial region, the ilepth beliind tin's is sometimes only 0' .j °o of the length of the body. 



'' 1(V:! is the least percentage we have found for this relation. 



*■ .\n exception is adduced by Kroyek in the largest Lampeni measured by him. The variations may be dne, however, to the dif- 

 ferent degree of contraction in the snout and dorsal muscles at death or in alcohol. 



■'' In the preceding species 68 — 75 %. 



'■' T'he dental differences in these respects are so variable that we have not been able to reduce them to any nile; but it would appear that speci- 

 mens from (lie sea or with only intnmescent genital organs and not yet shrunken intestinal canal most often have the most pointed .and whitest teeth. 



