246 Part III.—Ticentieth Anymial Report 



first anal fin. It commences furthest forward in the Ij'the, next in the 

 saithe, and furthest back in the cod. It ends soonest in the cod, then in 

 the lythe, and last in the saithe. The lengths of the bases of this fin in 

 the three species are — cod, 17-8 ; saithe, 27 ; lythe, 30-4 per cent, of the 

 length of the fish. 



Second Anal Fin : — In the cod and the lythe the second auals begin 

 together, and in front of that fin in the saithe. This fin ends first in the 

 cod, next in the lythe, and last, and that at a considerable interval, in the 

 saithe. The base of the fin measures — cod, 11-8; saithe, 12-9; lythe, 

 12'6 per cent, of the total length of the fish. 



The fiuless part of the peduncle (ventral edge) measures in the cod 2-7, 

 in the saithe 3-4, and in the lythe 3'3 per cent. 



Base of Tail : — The base of the tail is further forward in the cod than 

 in the lythe, and in the latter it is in front of the same part in the saithe. 

 The dorsal and ventral origins of the tail are at about the same level. 



Rami of Tail :— The, rami of the tail, both dorsal and ventral, in the 

 lythe and saithe project behind the ends of the middle rays of the tail. 

 In small cod, e.g. 46 cm., they project a very little beyond the middle 

 rays, but in adult cod the middle rays project the furthest back. The 

 tail then in the adult cod is rounded gently outwardly ; in the saithe and 

 lythe it is forked. It is much more deeply forked in the saithe than in 

 the lythe. 



The condition in the cod might be imagined to result from the 

 condition in the saithe by a forward transference of the rays of the 

 dorsal and ventral lobes of the tail. All the dorsal fins and the 

 second anal fin of the cod are carried further forward than in the 

 saithe. The hind extremity of the first anal also occupies a more 

 anterior position in the cod than it does in the saithe. The further 

 posterior position of the anus in the cod simply reduces the length of the 

 first anal fin. So that we have in the cod an anterior transference of the 

 unpaired fins, to such an extent that the lobes of the caudal fin, ■which in 

 the saithe project backwards into two prominent rami, now occupy a 

 position in which their hind edges project little or none at all behind the 

 tips of the middle tail-rays. In the lythe we have an intermediate con- 

 dition. In this form the third dorsal, first and second anal fins, and the 

 bases of the caudal fin are well in front of those parts in the saithe. The 

 fork in the tail is thus much shallower than in the saithe. 



Lateral Line : — The lateral line in all three forms is straight in its hind 

 third, i.e. from the base of the tail fin forward to about the middle of the 

 first anal fin. In this region it begins to bend upwards. In the cod and 

 lythe it turns rapidly upwards, and runs in a curve forward to the level 

 of the pectoral region. In the saithe it begins to rise near the hind end 

 of the first anal fin, and proceeds very gently upwards in a straight line 

 to its greatest height in the pectoral region. The point at which the 

 lateral line turns upwards is furthest forward in the lythe, next in the 

 cod, and furthest back in the saithe. In the lythe it rises more rapidly 

 than in the cod, and at the anus it is further up on the side of the fish 

 than it is in the cod and saithe, but just over the base of the pectoral fin 

 it is highest in the cod, next in the saithe, and least in the lythe. The 

 height of the lateral line at these two points is measured above the level 

 of the hind straight third of the line. 



The Vertebrae. 

 The cod has the smallest number of vertebrse, viz., an average of 5 TO, 

 while the lythe has an average number of 53 "4, and the saithe an 

 average of 5 4' 8 vertebrae . 



