6 BUU-ETIN OF THE BUREAU OF FISHERIES. 



to migration, is necessary. The author has attempted, therefore, to give in this report 

 as complete an account as possible of the early history of the chinook salmon. Im- 

 portant as these observations are, they are merely preliminary to the still more im- 

 portant study of the adult fish. Abundant material is at hand for this purpose, and 

 the author hopes to present in the near future a report covering those problems which 



relate to the adult fish. 



METHODS. 



The methods usually employed at the present time in studies of the life histories 

 of fish by means of scale analysis have been followed. 



The length of the fish was determined by laying the specimen flat on a rule and 

 measuring from the tip of the snout to the end of the middle rays of the caudal fin. 

 These measurements were made in millimeters. 



In counting the number of rings (circuli) on the scales the count has always been 

 made in the anterior quadrant of the scale, since the number of rings has been found 

 to be less variable there than in the lateral quadrants. The different areas of growth, 

 such as the summer and winter bands (annuli), are also more sharply differentiated in 

 the anterior quadrant. 



Any measurements of scales and portions of scales which are given, were 

 made by means of a camera lucida. The apparent image of the scale projected to the 

 level of the base of the microscope was measured by a millimeter rule. There is ob- 

 viously no significance to the actual size of this apparent image, since this would vary 

 with the degree of magnification employed. The only value such measurements have 

 is for comparative purposes. Therefore, the units of measurement have been considered 

 as purely arbitrary, and no actual value is assigned. It seems hardly necessary to state 

 that the same magnification has been used throughout this study. The actual mag- 

 nification of the image was approximately X 120. This would give an actual value 

 of 0.00834 mm. for each unit of measurement. The measurements as given in the 

 tables were made from the center of the iimermost ring along the anterior radius of the 

 scale. 



One method of study used has not, to the author's knowledge, been previously 

 described. This is the employment of large series of photographs for the purpose of 

 deciding doubtful points. It not infrequently happens that the scales from different 

 lots of fish will vary consistently in one or more minor characters which are very difficult 

 to determine by the successive examination of scales from individual fish. The memory 

 seems incapable of carrying all the necessary details in such form that a logical con- 

 clusion could be reached. When, however, fairly large series of photographs, say 50 

 of each category, can be spread out side by side, the comparison may be made very 

 readily, and often important conclusions may be drawn. 



After some experimenting, in order to reduce the expense of plates, printing, etc., 

 the scheme finally adopted for this purpose was to photograph directly on paper. Bro- 

 mide paper was tried at first, but it did not prove satisfactory. Either Azo, F, hard X, 

 or contrast Cyco was finally found to give the best results. Since the light values have 

 no particular significance in scale photographs, where the main requirement is to show 

 the lines well, these paper negatives are as favorable for study as prints taken from plates 

 would be. In case duplicates are wanted, these negatives may be used in the same 



