866 



the (lisfaiice between the ventral tins and the tip of 

 tlie snout. Accordingly too Osmenis, as a representa- 

 tive of one of the earlier stages of the family, has 

 greater averages in these respects than the Salmons. 

 This is also the ease with the length of the base of 

 the anal tin". A general rule for the whole life of the 

 Salmonoids is that the lengtli uf the niaxillaries is re- 

 duced with age in proportion to that of the body', 

 and the same rule applies to the length of the sub- 

 opei'culum in proportion to that of the head or of the 

 head reduced'', with a slight exception in the last case. 

 The breadtii of the interorbital space, on the contrary, 

 increases with age in proportion to the length of the 



SCAXDINAVI.VX I'lSUES. 



head or of the head reduced 



The length of the pe- 

 duncle of .the tail at the ventral margin', and the least 

 depth of the tail', in proportion to the length of the 

 head or of the head reduced, undergo alterations of 

 growth which at the modification in the life of the 

 Salmons — from fresh water to the sea — change di- 

 rection: their averages increase as a rule in the earlier 

 and earliest stages, but subsequently decrease, after 

 attaining their maximum at the end of the life in 

 fresh water. Here too Osmerus represents the earliest 

 stages. 



Arithmetically expressed, this developmental rela- 

 tion appears as follows: 



Di^taa^■c■ lietween the dorsal tin ami the tip of the snout in fS of the length of the body 



„ ., „ ,, ,, „ „ ,, distanee between the ventral tins and the tip of the snout. 



Base of the anal fin in ?» of the length of the body... 



,, ., „ „ ,, .. ,, ,, ,, ,. ., „ head rediieed 



Length of the maxillarics in ". of the length of the body : 



„ „ „ suboperculum ,, ,, „ „ ,, ,, „ head - 



,, ., ., „ „ „ ,, „ ,, „ „ head reduced 



Breadth of the interorbital spaee in % of the length of the head 



,, ,, ,, ., ,, „ ,, .. ., ,, ,, ,, head reduced 



Length of the peduncle of the tail at the ventral margin in % of the length of the body 



Lcost depth of the tail in % of the lenglh of the head 



„ ,, „ head reduced 



In other ].>oints, agtiiii, it tippears that the Smelts 

 and tlie Salmons have each taken their own path 

 of evolution, and that the Smelts in several respects 

 — in some like the Charrs — occupy the higher rank 

 in the scale of development. (.)n continuing our search 



for the most different averages in the Smelts and Sal- 

 mons, and on comparing the signification thereof with 

 the alterations of growth to which the Salmons are 

 subject, we find the following relations most deserving 

 of notice: 



" Cf. Smitt, 1. c, p. 14. 



'' „ ., ,. „ P- If- 



' ,, ,, „ „ PP- 1^ iin'l ■^-■ 



'' „ „ „ „ PP- 17 aii'l ■•20. 



' „ „ ., ., p. l.'^. 



'' Cf. above, p. 833, the lower table, where these proportions iiiiiy ea>ily be calculated from the av 



Riksmus. 'Salnionider, pp. 19 and 23. 



there given, and Smitt, 



