21 



other words the life of the eel is marked by an extreme periodicity, much strouger 

 than that iu the fishes, the scales of which have been mentioned above. We can 

 ah-eady eonclude from what has beeu said, that the growth of the eel in this 

 resting period either ceases entirely or is in any case extremely small. This is 

 shown directly by a comparison of the eels taken in autumn and in the following 

 spring, before growth has recommenced (see Tables 1 and 2). Table 1 has been 

 taken from the above-meutioned paper by A. C. Johansen. Table 2 and all following 

 Tables ara based on the investigatious of the Biological Station in the summer of 

 1906. It is seen at once from Tab. 1 that the group (year-group) which has its 

 maximum at 8 cm. is found both in autumn and early in the following spring; 

 the eels of this group have not grown in the course of the winter; and the con- 

 ditions will be the same for the individuals of the other year-groups. This is also 

 seen indirectly from Table 2. The I. group (with maximum at 11 — 12 cm.) in 

 column 2 (autumn) is met with in spring at the same size (column 3); it can 

 scarcely cause any error if it is now cailed the II. group. — For the rest, see the 

 following description with regard to the »groups«. 



The possibility is thus present, that not ouh^ the growth of the eel itself 

 but also, for example, the growth of its scales is marked by this periodicity; it is 

 indeed not improbable that the stoppage in growth also iudicates a stoppage in 

 the growth of the scales, which is expressed in their structure — and what has 

 been said above ou the matter iudicates further that this is really the case. 



We have seen (p. 14) that Baudelot had already suspected a connection 

 between the size of the scales and the size of the eels and states: »The dimensions 

 of the scale show variations which — with all due reservation — are so distinct 

 that they might seem to be dependent upon the age of the lish.« And in describing 

 the zones of the scales he says quite en passant: »The zones perhaps represent 

 zones of growth«, but he does not inquire further iuto this question. 



Independeut of Baudelot, C G. Joh. Petersen also mentioned the matter and 

 expressed clearly the idea, that the zones, which he cailed growth-streaks , were 

 possibly to be considered annual rings. Iu the Report of the Biological Station, 

 V. 1894, this author writes: »About this length, ca. 200 mm., the eels begiu to 

 have scales, previously they are naked. The scales appear first near the lateral 

 line, they are somewhat elongated and show growth-streaks, which possibly corres- 

 pond in number fairly exactiy to the years passed; this is a matter however which 

 requires further investigation.;: — Fiually, there is a statement by Stuart Thomson 

 who briefly mentions the scales of the eel iu his above- mentioned paper. He says: 

 »The scales of the eel show rings very clearly; but whether these are annual or 

 not I would not at present certaiuly determine, as I have not a complete series of 

 the fish. If the rings are annual, and from the faet that these animals seem to 

 have a wint«r sleep, it would be uatural to suppose that such is the case — 

 then . . . .« 



