52 THE PERIODIC GROWTH OF SCALES IN GADIDili; 



examined some time later, those from the pond sliowed an increase of scale 

 surface, with widely separated concentric lines, while those from the aquarium 

 showed little increase of scale surface and closely situated concentric lines. 

 The increase in the case of the pond fish he ascribes to the supply of plankton 

 food from the water. Another interesting case is that of carp whose growth 

 was partly disturbed for a time by an accidental drying up of the water in the 

 pond in which the carp was living. On the scales of this carp being examined 

 some time after the renewal of the supply of water, the effect of the partial 

 drying up and subsequent renewal of the water appears marked out in the 

 scales, the adverse condition by dark closely situated lines lying close together, 

 the normal condition by clear and more widely separated lines. During the 

 partial drying up of the pond, the fish were probably deprived of their wonted 

 nourishment. 



In conclusion, he deals with the case of an invalid carp. "When this carp 

 was caught it appeared thin and poorly nourished. On examination this 

 appeared to be due to a swelling in the anal region. The scales seemed 

 clearly to show at what time this, swelling had effected a disturbance in the 

 growth of the animal. He concludes his first paper on this subject by saying 

 that age-determination from the scales will not probably be so easy in carp 

 older than three years, as the older the carp becomes the larger and thicker 

 do its scales become, and consequently they are not so transparent, and 

 recognition of the concentric strise becomes more difficult, especially in the 

 first year's zone surrounding the centre of growth. 



In the following year Dr. Hoffbauer issued a second paper, a continuation 

 of the last noticed. His subject is now somewhat Avider, namely, "Further 

 contributions on the structure of fish scales for determination of the age 

 and course of growth."* In this paper Hoffbauer strengthens his position 

 by means of further results and statistics, and also replies to certain criticisms 

 by Dr. Walter {Jaliresherichtes in der Fischerei Zeittmg, Bd. iii., 1900, Nr. 19). 

 "Walter had allowed the general correctness of Dr. Hoffbauer's observations, 

 but had regarded them as less certain and easy of recognition for practical men 

 than for Dr. Hoffbauer. 



Hoffbauer regards "Walter's position as largely due to unnecessary methods 

 Avhich he employed in cleaning scales, by which the characteristic features of 

 the scale became less apparent. 



In this second paper Hoffbauer, in addition to extending his observations 

 -on the scales of the two varieties of carp treated of in his first paper, includes 

 those of Carasshis carassiiis, L., Micropterus sabna'ides, and Perca lucioperca 

 in his observations with equally good results. 



In January, 1902, I published a preliminary paper on the same subject as 

 my present contribution. t 



From this paper I quote the following paragraphs : — 



"The formation of these annual rings results from the fact that the lines of 

 growth on the scale surface are comparatively widely separated from one 

 another in that portion of the scale formed during the warmer season of the 

 year ; but much less widely separated in that part built up during the colder 



* HofTlianei-, 1901. t Thomson, 1002. 



