374 PERIODIC GROWTH OF SCALES IN GADID.*! AND PLEURONECTID^i, 



since they permit the extension to marine fishes of a new system of 

 age determination by means of these annual rings on scales, a system 

 which has recently been shown and demonstrated by Dr. Hoffbauer for 

 the carp.* 



I hope to illustrate clearly the mode of formation of annual rings in 

 Gadoid scales by the aid of the figure on the accompanying plate. 



The figure (Plate V., Fig. 1) represents the scale of a pollack, 28*5 centi- 

 metres (11| inches) in length, captured towards the end of October. A 

 minute translucent area (see Fig. 1, C) devoid of any lines is situated 

 towards the narrower and more internal end of the scale ; and around 

 this area, which is the first portion of the scale to be formed, are 

 grouped numerous excentric lines of growth similarly disposed to the 

 excentric layers in the starch grains of the potato. 



The excentric lines of growth on this scale, however, are arranged in 

 such a manner (see figure) as to map out its surface into two main 

 regions, namely, an internal area, which is the entire growth of the 

 first year, and an external part, the summer growth of the second 

 year. One understands how these two areas appear so distinctly if one 

 follows the lines of growth outwards from the translucent area to the 

 broader and more external part of the scale. One may firstly observe 

 that there are nineteen lines comparatively widely separated from 

 one another, which indicate the growth of the first summer, and 

 secondly, ten lines less widely separated, indicating growth of the first 

 winter. External to these, there follows an area showing much more 

 widely separated lines of growth, which indicate the scale growth 

 of the second summer. 



The difference between the lines of growth formed during the second 

 summer and those of the preceding winter is so apparent as to clearly 

 define the termination of the first year's growth. The widely separated 

 lines of the second summer number nineteen, and as the pollack 

 from which this scale was taken was captured in October, it appears 

 that in this scale the number of lines formed during the second summer 

 exactly agrees with the number formed during the first summer. 



In most cases, however, the growth of the scale in the pollack's 

 second year appears to be greater than that of preceding and succeed- 

 ing years. As the statistics of the forthcoming paper are too detailed 

 for the purposes of this note, I select a few tabulated figures relating 

 to Gadus 2')ollachius and Gadus vmuitus, which will in some measure 

 show the general bearing and object of this work. The following tables 

 commence with fish about an inch in length, the scales of which show 

 a small translucent area without any lines of growth (excentric lines), 



* " Die Altersbestimmung de3 Karpfen an seiner Schuppe," von Dr. Hoffbauer ; 

 Jahresbericht des Schlesischen Fischerei- Vereins fiir das Jahr 1S99. 



