IX] OF FISHES' SCALES AND OTOLITHS 433 



where the temperature and other physical conditions shew httle 

 or no appreciable fluctuation with the seasons of the year. 

 There are, on the other hand, phenomena which seem strongly 

 confirmatory of the hypothesis : for instance the fact (if it 

 be fully estabhshed) that in such a fish as the cod, zones of 

 growth, identical in mimher, are found both on the scales and 

 in the otoliths*. The subject has become a much debated one, 

 and this is not the place for its discussion; but it is at least 

 obvious, with the Liesegang phenomenon in view, that we have 

 no right to assume that an appearance of rhythm and periodicity 

 in structure and growth is necessarily bound up with, and 

 indubitably brought about by, a periodic recurrence of particular 

 external conditions. 



But while in the Liesegang phenomenon we have rhythmic 

 precipitation which depends only on forces intrinsic to the system, 

 and is independent of any corresponding rhythmic changes in 

 temperature or other external conditions, we have not far to seek 

 for instances of chemico-physical phenomena where rhythmic 

 alternations of appearance or strvicture are produced in close 

 relation to periodic fluctuations of temperature. A well-known 

 instance is that of the Stassfurt deposits, where the rock-salt 

 alternates regularly with thin layers of " anhydrite," or (in 

 another series of beds) with " poly halite f " : and where these 

 zones are commonly regarded as marking years, and their 

 alternate bands as having been formed in connection with the 

 seasons. A discussion, however, of this remarkable and significant 

 phenomenon, and of how the chemist explains it, by help of the 

 "phase-rule," in connection with temperature conditions, would 

 lead us far beyond our scope J. 



We now see that the methods by which we attempt to study 

 the chemical or chemico-physical phenomena which accompany 

 the development of an inorganic concretion or spicule within the 



* Gf. Winge, Me.ddel. fra Komm. for Havundersogelse (Fiskeri), iv, p. 20, Copen- 

 hagen, 1915. 



.f The anhydrite is sulphate of lime (CaS04) ; the polyhalite is a triple sulphate 

 of lime, magnesia and potash (2CaS04 . MgS04 . K2SO44- 2H2O). 



t Cf. van't Hoff, Physical Chemistry in the. Service of the Sciences, p. 99 seq. 

 Chicago, 1903. 



T. a. 28 



