666 ON CONCRETIONS, SPICDLES, ETC. [ch. 



as a trustworthy and unmistakeable measure of the- fish's age (see 

 ante, p. 180). There are some difficulties in the way of accepting 

 this hypothesis, not the least of which is the fact that the otolith- 

 zones, for instance, are extremely well marked even in the case of 

 some fishes which spend their lives in deep water, where temperature 

 and other physical conditions shew little or no appreciable fluctuation 

 with the seasons of the year. There are, on the other hand, pheno- 

 mena which seem strongly confirmatory of the hypothesis: for 

 instance, the fact (if it be fully established) that in such a fish as 

 the cod, zones of growth^ identical in number, are found both on 



Fig. 307. A sphero- 

 crystal of" inulin. 



Fig. .*i08. Otoliths of plaice, shewing 

 four zones or "age-rings." After 

 Wallace. 



the scales and in the otoliths*. The subject is as difficult as it is 

 important, but it is at least certain, with the Liesegang pheno- 

 menon in view, that we have no right to assume, without proof 

 and confirmation, that rhythm and periodicity in structure and 

 growth are necessarily bound up with, and indubitably brought 

 about by, a periodic or seasonal recurrence of particular external 

 conditions^. 



But while in the ordinary Liesegang phenomenon rhythmic 



* Cf. Winge, Meddel. fra Komni, for Hav under sogelse {Fiskeri), iv, p. 20, Copen- 

 hagen, 1915. 



t A. VV. Morosow strongly supports the view — uncertain as it seems to be — 

 that the concentric pattern of a fish's scale is due to the Liesegang phenomenon; 

 he produces an "artificial scale," with its "summer and winter rings," by 

 precipitating sodium carbonate and calcium chloride in gelatin: Zur Frage iiber 

 die Natur des Schuppenwachstums bei Fischen (and in Russian), Nation. Comm. 

 Agriculture: Rep. Sci. Inst. Fisheries, i, Moscow, 1924; abstract in Michael 

 Graham's Studies of age-determination in fish, Rep. Ministry of Agr. and Fisheries, 

 Fishery Investigations, (2) xi, no. 3, p. 28, 1928. 



