*)04 



SCAM) IN AVIAN FISHES. 



Vendace, varying on an average aliout 7 % (in polciir 

 about 8 %, in tsclvir nearly 9 %) of the lengtli of the 

 body, between ?>?> and 40 % (in polriir 41 — 4") %, in 

 tschir 52 %) of tlic Icngtli of the head, or between 44 

 and ')2 % (in polcKr .")6 — til %, in txehir !'.'> %) of tlie 

 length of the head reduced. Some Gwyniad forms 

 may indeed be said to be cliaracterized by a shallow 

 tail (an elongated bodv); l)ut it sliould be observed 

 tliat this character is also a cliai-iicter of age. Conse- 

 (|uently it happens that, in certain lakes, especially in 

 Lake Bolmen in Smaland, where it has longest l)een 

 known, but also in many other lakes from Lapland to 

 Smaland, we meet with a Gwyniad f(jrra (Nilsson's 

 Coregonits lavaretKs. Malm's forma holmensls) Avhich 

 differs, so far as we knoM'^xonstantly from the ;illied 

 forms in the shallow pedu^PI of its tail. But in other 

 waters, for examjile in the system of small lakes in 

 Smaland which falls into the Baltic through the River 

 Morrum, this very form is developed into the form 

 with deeper tail, \vhich else has its most typical repre- 

 sentative in the Lake King (-rwyniad (Valenciennes' 

 Corecfonus NUssouii). The bldsikar in the uppermost 

 of the said lakes — Helga and Bergunda" — in most 

 respects afford mii instructive example of the cliaiiges 

 of growth througli which the Gwyniad passes in the 

 less advanced stages of its form-series. In particular 

 they show how the least depth of the body, the most 

 distinctive character of bolmensis, increases with age so 

 as to apjjroach the typical Coreffoniis NUssonii. In 

 Asnen, a Inke of greater size and situated nearer the 

 outlet of the system, the NUssonii type' is developed 

 at an eai'lier age (a smallei- length) than in the two 

 said lakes. In this locality it therefore seems that 

 Cor. bolmensis should really be regai-ded as a young 

 stage of Coi: NUssonii, which in other places, for ex- 

 ample in Lake Bolm, may persist as a separate form. 

 The deeper form of the bodv is most often accom- 

 panied by a special arrangement of the scales that 

 gives the tish a singular appeai'ance. When the skin 

 is distended, the rows of scales part from each other", 

 and the exposed portion of each scale becomes hexagonal 

 instead of semirirculnr. The (j^wyniad then displays a 



striking resemblance to the Grayling. In the bldsikar 

 — but especially in the typical Lake Ring Gwyniad — 

 we also find a special form of scale, at least in the 

 rows nearest to the lateral line, the free (hind) margin 

 of the scale becoming more or less elongated at the 

 nuddle (forming a rounded obtuse angle instead of a 

 circular arc). But in all the Gwyniads examined by 

 us this difference also appears l)etween the scales on 

 the sides of the tail and those on the forepart of the 

 body. The cliaracter assigned by Lilljeboiu; to Core- 

 fjonus NUssonii, that the exposed |);irt of the scale in 

 the rows nearest to the lateral line is more than half 

 as long as high, may be found in most Gwvniads, at 

 least in solitary scales. 



While it often happens, esjjeciallv auK.ing the Ijld- 

 sikar, that the comparatively great size of the eves is 

 persistent longer than usual — a relation which Wini:- 

 GREN expressed bj' establishing a separate species, Corc- 

 (jonns megalops — the fetslkar run to the opposite ex- 

 treme, the reduction in the relative size of the eves 

 during growth proceeding more rapidlv and advancing 

 further than usual. The form produced in this man- 

 ner we have called microps, less in order to indicate 

 the importance of the difference as such, than because 

 it is usually accompanied by an increased fatness which 

 has rendered the form econon^icallv important. It 

 occurs, according to the collections of the Royal Mu- 

 seum, in the Gulf of Bothnia, the rivers of Norrlaud, 

 Lake Wener, and Boliuslan. Maliicren sent home 

 specimens of a similar form from Lake Ladoga. The 

 same importance is shared by ani^thcr form, from the 

 Angerman and Torne Elfs, wliich is characterized by 

 a comparatively small head, and which we have there- 

 fore named microcephnlus. 



None of these forms seenus quite to deserve the 

 rank of an independent variety. They sometimes appear 

 to occur alone, liut as a rule at least two are found 

 in the same lake or river — Lake Wener possesses at 

 least 7 of these forms — and that they intermingle 

 during the s])awning, is more than probable. But as 

 a rule a distinction may be drawn between them in 

 the followini;' manner: 



" Smitt, 1. c, tnb. metr. XI, N(is. 210— 215. 



'■ 1. c, Nos. 216 and 217. 



'" A striking example of this is Siebold"s figure of Corecjonus acronius (Siisswasserf. Mitti^lcur., taf. II), inoiistrously swollen owing 

 to tlie expansion of the air-bladder when the fish was drawn up from deep water; but the same appearance is almost as marked in gravid 

 females. We have above seen a similar difference in the appearance of the scales among the Perches for example: — cf. the Carass Perch 

 (tig. 3, p. 29) with the oommon Porch. 



