244 



Pari III. — Twentieth Annual Report 



Table VIII. 



Length of the Bases of the Unpaired Fins represented as Percentages of 

 the Length of the Fish, taken from the Tip of Premaxilla to end 

 of Middle Ray of Tail. 



Comparison between the Cod, Saithe, and Lythe. 

 (Plate VIII.— Cod, Fig. 7 : Saithe, Figs. 5, 8, 11 : Lythe, Figs. 6, 9, 10.) 



The comparison between the three species is made then by means of 

 the averages given in Table VII. Taking the characters in the order in 

 which they are set down in the Table, we may at a glance see the general 

 inter-relations of the three species. 



Girth : — It is useful to consider the girths at the pectoral region and at 

 the anus together. The cod has a greater girth in the pectoral region than 

 at the anus ; while in the saithe and lythe the anal girth is greater than 

 the pectoral. The girth at both points in the lythe is greater than in the 

 saithe. The greater girth in each of the three species is just over 50 per 

 cent, of the length, while the less is a little under 50 per cent, of the 

 length. The cod and the saithe bear an inver-se relation to one another ; 

 by simple transposition the girths of one form are converted into those of 

 the other. 



As regards the girth of the caudal peduncle, the cod and the saithe 

 agree closely ; while the girth of that part in the lythe is considerably 

 greater than it is in the two former. 



Dorso-Ventral Height :, — In this character practically the same relation- 

 ship is seen between the three species as was found to exist in respect to 

 girth, 



T^engths of Paired Fins .-—In the matter of the lengths of the paired 

 fins very definite diflferences exist between the three species. In the cod 

 and the lythe the pectoral fins are of similar length, and a little greater 

 than that of the saithe. The ventral fins differ in the three forms ; and 

 it is by means of the ratio between the lengths of the ventrals and pectorals 

 that the differences are most readily described. Thus the ventral fin of 

 the cod is about five-sixths the length of the pectoral ; that of the saithe 

 is more than one-half and less than two-thirds of the pectoral ; while in 

 the lythe the ventral fin is less than one-half the length of the pectoral. 



Greatest Height of the Unpaired Fins : — The unpaired fins of the cod 

 are higher than those of the saithe and lythe, which are very similar to 

 one another. Those of the lythe are, however, with the exception of the 

 second dorsal, a little higher than those of the saithe. 



Tail Fin : — As regards the tail, the shape of which differs in the three 

 species, there is no agreement seen between the species in the measure- 

 ments which have been selected. In the cod the dorsal and ventral edges 

 (rami) are shorter than in the lythe and saithe, and of the latter two, those 

 of th'^, lythe are shorter than the tail-rami of the saithe. While in the 

 saithe and lythe the tail is forked, in the cod it is practically straight across. 



