AS AN INDEX OF AGE. 51 



One does not need a detailed observation such as the above to distinguish 

 a slow-growing carp of three summers from a well-grown carp of two summers, 

 as superficially the difference in the distance of the concentric lines, in such a 

 two-year carp of approximately the same size, is distinctly greater at its chief 

 period of growth, and besides this, the age border between the first and 

 second year is also much more distinct. "With practice one can in a similar 

 way distinguish between a slow-grown carp of two summers and a quickly 

 grown carp of one summer. The age-determination of rapidly grown carp 

 offers no difficulty, the difference in the distance of the concentric striae appears 

 distinctly prominent at the time of the growth period. One may lay down the 

 following general rule in regard to the relationship of the concentric lines : — 



" Je mtensiver das Waclistum der Karpfen, I'esj^eJdive seiner Sclmppe, um so 

 grosser wird der Ahstand der Iconzentrischen Streifen von einander und umso 

 vnregelmdssiger, unzusammenhdngender ihr gegenseitiger parallel Verlauf." 



He shows, from his figures that from spring until the height of growth in 

 the summer months a steady increase of the distance of the concentric striae 

 appears, which finally are represented as zigzag lines partly anastomosing with 

 each other. In autumn the lines become much closer to one another, until 

 finally they become extremely close and regular. In some cases in the first 

 year's zone, in consequence of a great expansion of the centre of growth, con- 

 centric lines are not formed in spring-time, but only in summer-time. 



Under some circumstances, however, an intensive growth may take place in 

 spring-time, as shown in fig. 6 (Hoflfbauer). This figure shows that the con- 

 centric striae at the commencement of the second year have a very regular 

 course and are at a great distance from each other. In other figures he shows 

 how much the centre of growth may expand; thus in fig. 8, representing the 

 scale of a one-summer carp, only twenty irregular concentric lines have been 

 formed at the conclusion of the growth period, while under normal conditions 

 fifty to sixty and more are to be seen. Further, in fig. 9 the first year's zone 

 is altogether without concentric lines, which only commence their formation at 

 the beginning of the second year. Even the second year's zone may have no 

 concentric lines, as he shows in his tables giving the number of concentric 

 lines ; this is, however, a rare occurrence. 



The remainder of his paper is taken up with a consideration of photo- 

 micrographs of scales from carp bred in pond or aquarium, for all of which he 

 had exact knowledge as to their age and history, and to my mind these figures 

 show in a very clear and interesting manner the truth of this mode of age- 

 determination. He shows that in carp, the scales of which were periodically 

 examined, the increase in the dimensions of the size of the scales, the number 

 of concentric lines formed in them, and the amount of separation between the 

 lines, corresponded with the known facts as to whether the fish were slowly or 

 quickly gaining weight, and this in a very striking manner. He says, '* Die 

 Unterschiede sind so deutlich erkcnnbar, dass wir uns eine bessere und 

 untrugliche Orientirung gar nicht verschaffen konnen." He further takes up 

 the case of two carp of the same brood and of equal weight ; one of these was 

 put into an aquarium, the other into a pond at the same time, their scales 

 being first examined. The carp placed in the pond naturally gained weiglit more 

 quickly than that placed in the aquarium, and on the .scales of botli being 



