42 



SCANDINAVIAN FISHES. 



forehead, one on each side of either nostril. One row 

 of cavities runs alon<r the cheek, and another on the 

 margin of the preoperculum is continued along the lower 

 jaAv. In front of all, on each side of the tip of the 

 snout, is a little, round hole through which the system 

 of ducts has free communication with the sun-ounding 

 water. The operculum and preoperculum, as well as 

 the shovdder-girdle (the post-temporal and clavicular 

 bones) are armed ^\■ith spines. The mouth is of average 

 size, and the upper jaw projects slightly over the lower. 

 There are several rows of very fine and closely set 

 teeth on the ja^vs and the anterior portion of the palate, 

 and also 4 pharyngeal patches of teeth, 2 upper and 2 

 lower. The nasal sacs are fairly elongated and are 

 situated about halfway between the tip of the snout 

 and the anterior orbital margin. The anterior nostril 

 is tubular and round and is furnished Avith a mem- 

 branous flap, the posterior is lai'ger and oval and is 

 without a cover. Tlie eyes are fairly large, their lon- 

 gitudinal diameter is in older specimens 24 or 25 % of 

 the length of the head, in younger about 29 %. In the 

 former this diameter is equal to the distance between 

 both the posterior nostrils, in the latter greater than it. 

 The iris is vellow, the lens blue. When the fish has 

 been out of the water for some time, however, the lens 

 turns a whitish l)lue-green, something like the appea- 

 rance known as wall-eye. The lateral line is near the 

 back and follows its curve. In the anterior portion of 

 the l)()dy it pierces the scales oblicjuelv do\vnwards in 

 a longitudinal direction, so that the anterior scales in 

 tills line are dentated at the posterior margin only above 

 the ducts of the lateral line, and are also posteriorly 

 emarginate. Nearer the tail the ducts of the lateral 

 line pierce the scales nearer their centre and follow 



their direction exactl}', so that the hind margin is den- 

 tated both above and below the incision we have just 

 mentioned. The belly is yellowish white and flat, as is 

 also the breast, which is silver-white but shifts in colour 

 like mother of pearl at the death of the fish and finallj- 

 becomes rose-red. In the dorsal fin there are from 2.5 

 to 27 rays, and of these the posterior ones, from 10 

 to 13 in number, are soft and branched, while the rest 

 are strong and pungent spinous rays. In the pectoral 

 fins there are, as a rule, 14 or 15 rays, and of these 

 the two highest, and generally the two lowest as well, 

 are undivided but articulated. In colour these fins are 

 grayish }ello\v ^vith fine, dark dots forming transverse 

 bands. The ventral fins are almost Avhite and Avithout 

 spots. The anal fin resembles the ventral fins in colour 

 or sometimes has just a few dark spots upon it. As 

 a rule, it contains only 2 spinous ra}-s, and, a strange 

 exception to the general rule, the first of these is con- 

 siderably longer and stronger than the other. In the 

 specimen which has 3 spinous rays in this fin, the first 

 is little more than half as long as the second, Avhich 

 is the strongest and longest. The caudal fin, which is 

 grayish yellow -with dark spots arranged in transverse 

 bands, is deeply forked. 



The internal organs of this fish are very like those 

 of the Perch, with the exception of the fact that in 

 the female the roe-sac is double, though its parts are 

 united posteriorly. The number of the vertebrae is 37 

 and of the ribs 15. 



We know just as little of any constant, external 

 distinction between the sexes in the Pope as in the Perch 

 and Pike-perch, Init difference of age involves conside- 

 rable changes in form, and some of the most important 

 of these may be traced in the following table: 



Lc-Dfrth of the boilv from llip tip of the snout to the end of the middle riu's of the i-audiil tin mm. 



Length of the head in ./, of the length of the l)ody 



Longitudinal diameter of the eye » • » , , > » 



Base of the dorsal tin »»»« » »>» 



Spiuous-rayed porlion of the dorsal tin _ > > j > . > » » 



Base of the anal fin , , , , , , , , 



Distance between the insertion of the ventral tins and the beginning of the anal tin . > » > , ,. » 



Length of th<r ventral fins . j » » ■, i > , 



Greatest depth of body » > > » , j , , 



least » » > J . , , . V . 



" 111 tin's siiociiiini wi' liud /). .-n,,! A.~, as well ax i\ iiiiiiil 



10 6 



T of juvenile ehnracters, c. g. the exceptional size of the head and of the eyes. 



