Scientific Investigations. 19 



round the fish. The ends of the thread are made to overlap, and they 

 are then cut across by means of a sliarp knife (Fig. 4). 



Fkj. 4. — Diagram of Herring to indicate positions of tlie 

 Girth INfeasurcnients. 



VI. Horizontal diameter of the iris and pupil. The iris is co- 

 exte?isive with the silvery iridescent region. The pupil is oval and 

 requires two measurements, viz., long and short axes. 



VII. Length of the pectoral fin, i.e. the distance from the articu- 

 lation of the first ray (dorsal side) to the most distant point of the fin. 



VIII. Length of the ventral fin, i.e. the distance from the articu- 

 lation of the first ray to the most distant point of the fin. 



IX. The greatest dorso-ventral height of the dorsal fin, when it 

 is spread out to its greatest extent. One point of the dividers rests 

 on the to]) of the interspinous bones between the bases of the fin-rays 

 immediately below the highest point of the fin. 



X. Length of the dorsal ramus of the tail fin, measured from the 

 point of beginning of ramus defined in XXVI. to the tip of the 

 ramus. 



Characters VII. to X. are measured by means of dividers. 



XI. The number of rays in the pectoral fin. 



XII. ,, ,, ,, ventral ,, 



XIII. ,, ,, ,, dorsal ,, 



XIV. ,, ,, ,, anal ,, 



XV. The number of keel-scales from and including the keel-scale 

 situated between the bases of the ventral fins to the anus. 



Distances of Certain Points from the Tip of the 

 Lower Jaw. 



For the following characters the herring is placed on the measuring- 

 board, so that tlie principal axis {i.e. the line drawn from the lower 

 edge of the turned-down lip on the anterior end of the lower jaw to 

 the middle of the fork of the tail) coincides with a line drawn on the 

 board, and also with the thread stretched longitudinally over the 

 board (Fig 5). The mouth of the fish is to be closed. It may be an 

 advantage to fix the fish by means of long needles passed through the 

 fish and into the board. The travelling T-square is moved along till 

 the thread (or horse-hair), the point on the fish, and the needle-point, 

 which is vertically below the thread, are, as near as the eye can judge, 

 in one plane. The distances are read off by means of the needle-point 

 which travels over the scale. 



XVI. Anterior edge of the pupil of the eye. 



XVII. Posterior edge of the flattened area on top of the head. 

 The hind edge of the transverse ridge (upper edge of supra-occipital 



