835 



scales, ex])res.st'd in tlicir nuinlicr. Tlu' scales are gene- 

 rally lai'ger in Sulmo siiUir tlian in .V. triilld, hnt larger 

 even in the lattci' llian in .V. iimhlii. In a longitudinal 

 vow extending along '/,,, of tlic lengtii of tiie l)ody, we 

 find 1) on the anterior part of the be]l_y above the la- 

 teral line in S. saliir on an average 18 scales, in iS'. 

 tnittd 18 — 21. and in S. taiihla :W, 2) on the tail in 

 iV. .sY(/((/' 1") or 1(), in .v. fridta I(! or 17, in S. iniiOla 

 20. Thus the Charrs ha\e proltahh' been developed 

 from a I'ace nearer to the Grnlax than to the Blankla.v; 

 but the development has followed the same course and 

 produced the same results in the differentiation of form. 



The natural relation between the Charrs is indeed 

 more complex, but all the more instructive. In Scan- 

 dinavia wc have two forms, the Northern (_'harr (Salmo 

 alpiiiKs) and tlie Sa'lbling (S. salrvliinist), whose right to 

 a specitie i'aid< is almost as certain as tlie difference 

 between the Grahi.r and the BlnnkJa.r, and which occupy 

 the same developmental relation to each other, S. alpi- 

 )ii(S representing the younger stages of growth, S. -ml- 

 vclinKfi the older ones. Besides these forms however 

 — in order to gain a correct understanding of the re- 

 lation between them — we mu.st take into consideration 

 a third form which strictly belongs to Greenland ;uid 

 the northern regions of North America, and for which 

 we may employ the specific name given it by Fabhi- 

 ciirs", Sabiio stagnaJis''. 



On closer examination of these three Charr forms, 

 we see that in many respects' the averages run in an 

 uninterrupted series from alpinus through stagnalis to 

 salreliiiKS, i. e. alpintis represents the youngest stages, 

 salveJiniis the oldest. Here, for the sake of brevity, 

 we can only give one example. 



The least depth of the tail in proportion to the 

 length of the head diminishes as a rule in the Charrs 

 with increasing age. In order more carefully to test 

 the particulars of this relation and others, I have di- 

 vided the material possessed by the Royal Museum 

 into six groups according to age. As we have no cor- 

 responding terms in popular phraseology, I have denoted 

 these groups by Roman numbers. The first group (I) 

 contains the specimens under 228 mm. in length. 

 Among all these specimens (of all forms and interme- 

 diate forms) the average length of the body is 18S mm. 



The second group (II) contains tlie Chai-r l)etween 228 

 and about ;555 mm. long. The average length of body 

 in this group is ?>(.)?> mm. In the tliird group (III) 

 the maximum length of \hh\\ is about ^.')!S mm. and 

 the average length .387 mm. In the fourth group (I\') 

 these measurements are respectively about ").38 nnn. 

 and 494 mm. Tiic fifth group (\') contains otd\' three 

 specimens, all about (i.')() mm. long. Tlie sixth group 

 (VT) consists of (jnly one specimen, a male from Spitz- 

 bergen, measuring 7.57 mm. 



The alterations caused 1>\' growth in the relation 

 between the least depth of the tail and the length ot 

 the head, are most regular in our s})ecimens of stag- 

 tialis, being in this form: 



The averages in the second group (II) are: 



aljjtnus. I staynalis. salvtUnus. 



I 37.1 



;34.o 

 :35.9 



"J! I 4 

 2i).9 



The form scries, expressed in averages for all our 

 specimens, is as follows: 



All these averages follow a regular course, con- 

 stantly decreasing. Such is the case where the form 

 series has retained its original type, and in the rela- 

 tions where the males evidently represent the highest 

 .stage of development. In several relations, however, 

 the females have a special representative in stagnalis, 

 and the original form series has thus been modified 

 in a singular manner. We have an example of this 

 in the proportion Ijetween the length (jf the ma.xillaries 



" Fauna Groenlandica, p. 175. 



^ In order to simplify the qneslioii, we here umil some intermediate forms, the significance of which wc may disreganl for the 

 time heing. 



' In the work quoted above (Rilcunus. Salmon.) I have adduced 18 such points. 



