LIFE HISTORY OF LAKE HERRING OF LAKE HURON 275 



and the scales superimposed upon thorn for portions of different scale rows on different 

 parts of the body, that the number of myomeres is usually less than the number of 

 the scales superimposed upon them. My corresponding or X scales were selected, 

 therefore, with reference to their general position on the body and not with reference 

 to any particular myomere. They were taken from the fourth longitudinal row 

 above the lateral line from the vertical drawn through the base of the first ray of 

 the dorsal fin. 



In the field a dozen or more scales were removed from each fish with forceps 

 and preserved in the standard scale envelopes furnished by the Bureau of Fisheries. 

 The fish were not preserved. The following data were then entered upon the face 

 of each envelope, if required: Species, locality, date, length, weight, sex, stage of 

 sex organs, gear, and collector. Wlien ready to mount, three or four of the dried 

 scales of each specimen were scrubbed clean in water. By use of a binocular micro- 

 scope care was taken that only typical and good scales were selected. The scales 

 were cleaned best with a small brush made of the stout ends of shoemaker's bristles 

 tied to a stick. The scale was held in place during the scrubbing by the blunt end 

 of a teasing needle, which was also employed to remove the more adhesive pigment 

 cells or dirt. \Vlien the three or four scales were cleaned, warm glycerin-gelatin 

 solution was placed on a clean glass slide in amount deemed necessary to cover 

 completely the scales placed in it. If the gelatin and the pure glycerin are mixed 

 in such proportion ^ that a small amount stiffens immediately upon cooling, and if 

 a liberal amount of the solution is used, no evaporation occurs under the cover glass 

 and the mounts may be kept permanently without sealing. Some of the photo- 

 graphs shown are of scales that had been mounted for two years. A little carbolic 

 acid must be added to the glycerin -gelatin solution to insure its preservation. 

 All scales were mounted with the circuli or rough side up and with the caudal area 

 toward the lower edge of the slide. 



The scale to be studied was projected upon the ground glass of an apparatus 

 constructed on the principle of a photomicrographic camera (Van Oosten, 1923). 

 All measurements of scales were made on this image, projected at a magnification of 

 19. On exploring the illuminated field covered by a scale image so magnified, I 

 found, by the use of a stage micrometer, that the magnification is everywhere uni- 

 form — there is no discoverable optical distortion. 



In measuring the projected scale, a wooden ruler was placed along the diameter 

 that bisects the caudal area of the scale (Lr-L, fig. 2) and readings were taken (to 

 the nearest millimeter) at the center of the focus, at each annulus in both the anterior 

 and posterior area, and at the anterior margin of the scale. More accurate measure- 

 ment was not found possible. I found, by scratching a line drawn parallel with the 

 long axis of the body on a longitudinal series of consecutive scales in situ, that the 

 line on all the scales followed the anteroposterior diameter defined above. This 

 diameter, therefore, gives more easily comparable measurements than any other. 

 The measurements were made use of in computing the lengths of fish by the formula 

 given on page 272. AU computations were made with a slide rule or with a Monroe 

 calculating machine. The circuli of the anterior area were enumerated along the 



* It was found by long experimentation that the fnlluwing formula gave the best results: Dissolve 8 ounces gelatin (WH, NOi 

 1866, Gcrmanyj in 850 cubic centimeters distilled water and add 250 cubic centimeters glyceria and a lew drops carbolic acid. 



