METHODS OF INVESTIGATION. 



These parr were hatched in March, 1898, and killed during the course 

 of the summer. 



From this we see clearly that the formation of rings advances with the 

 growth of the parr during the course of the summer, and that the scales 

 develop with the growth of the fish. 



The accompanying figure (Fig. 1) illustrates the scale of the largest 

 parr. If we examine it closely we note that all the inner growth rings go 

 regularly, and practically without a break, around the whole of the scale. 

 It is not until we come to the three outer rings that we find that the ring 

 formation begins to be broken. These latter 

 rings are only perfect on the anterior portion 

 of the scale (the upper portion of the figure), 

 and elsewhere they are merged in the edge 

 of the scale. It should not be forgotten that 

 this fish was killed in the late autumn. 



As a rule rings formed in the summer 

 are unbroken around the circumference of the 

 whole of the scale, though occasionally one 

 may meet with scales of which the summer 

 rings are not always complete. This probably 

 arises from the fact that all growths do not 

 proceed simultaneously, and that therefore 

 the different portions of the scale have not 

 always the same uniform rate of growth. It 

 is more than likely that this is due to some 

 variation in rate of growth in length and in 

 girth. In autumn and winter the growth 

 generally decreases or ceases entirely, and all 

 the scales I have seen show a similar edge 

 to the one illustrated. This character 

 is also retained during the whole of the winter, and such little growth 

 as does take place is shown in the production of narrower rings close 

 to the edge of the scale. After the winter, when development begins 

 again, the ring formation of the new season does not entirely coincide with 

 the last formed rings of the preceding season, and the new growth is shown 

 by the formation again of entire and unbroken rings. It is thereforejas a rule 

 easy to recognise the winter rings formed during the period of stagnation 

 between the two growth-zones. The chief characteristics of this period of 

 stagnation are the pronounced branching or ramification of the rings, and 

 also the fact that they are narrower and lie closer together, so that a mag- 

 nified representation of a scale shows a narrow and more darkly shaded 

 belt. This narrow winter-band has also a different optical refractive 



12 



FIG. 1. Parr 10 cm. Hatched 

 March, 1898. Killed Novem- 

 ber 1, 1898 (magnified). 



