BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 26. AFD. IV. N:0 8. 5 



From these relative measurements it can be seen that in 

 the common pikepercli the length of the head becomes greater 

 witli age. In this respect the Caspian pikeperch has a still 

 more advanced position, bnt the Volga-pikeperch retains a 

 ratber small head and it even seems as if it should be com- 

 paratively lessened with age. The enlargement of the head 

 in the common pikeperch seems to be eifected mostly by a 

 comparatively stronger growth of the postorbital region which 

 is, as it seems, gradually rather strongly enlarged. In the 

 Caspian pikeperch the development of the head has taken a 

 different conrse as in that species the preeorbital region is 

 the one that is comparatively larger. This indicates stronger 

 and larger jaws. In the Volga-pikeperch, as well the prse- 

 as more especially the postorbital dimensions of the head 

 compared with the total length are smaller than in the com- 

 mon pikeperch of corresponding size although it is most con- 

 spicuons with regard to the 1 ätter dimension. It is thus 

 apparent that concerning the development of the head the 

 Volga-pikeperch compared with the common species represents 

 a more juvenile and the Caspian a more advanced stage, al- 

 thongh in a manner a little modified. If we compare the 

 prfeorbital length with the length of the head we shall find 

 that in both the common and the Volga-pikeperch the former 

 dimension is 25, i % of the latter ^ but in the Caspian pike- 

 perch this relation is 29,2 %, thus a considerable difference. 

 The ratio of growth of the diiferent regions of the head can 

 also be fonnd by comparing the postorbital dimension with 

 the length of the head. We find then that in the two 

 younger Stizostedium lucioperca this percentage is 51,2 and 

 59,5, in the largest it is 63,9. The average percentage in all 

 six St. volgcnse is 55,2, thus a plainly juvenile character. In 

 St. marinum it is 57,7 the comparative smallness of which is 

 effected by the enlargement of the prseorbital region which 

 has prodnced a greater length of the whole head. 



In the common pikeperch the distance between the snout 

 and the anal fin is enlarged with age and in this respect 

 the Caspian pikeperch also is more advanced. This is a femi- 

 nine character as can be seen from the table concerning St. 

 rolgensc. The base of the first dorsal is larger, but that of 



^ It must be remembered here that the whole head is smaller in the 

 Yolga-form. 



