432 



ON CONCRETIONS, SPICULES, ETC. 



[CH. 



Among all the many cases where this phenomenon of Liese- 

 gang's comes to the naturalist's aid in explanation of rhythmic or 

 zonary configurations in organic forms, it has a special interest 

 where the presence of concentric zones or rings appears, at 

 first sight, as a sure and certain sign of periodicity of growth, 

 depending on the seasons, and capable therefore of serving as 

 a mark and record of the creature's age. This is the case, for 

 instance, with the scales, bones and otohths of fishes ; and a 

 kindred phenomena in starch-grains has given rise, in like manner, 

 to the behef that they indicate a diurnal and nocturnal periodicity 

 of activity and rest*. 



That this is actually the case in growing starch-grains is 

 generally believed, on the authority of Meyer f ; but while under 

 certain circumstances a marked alternation of growing and resting 

 periods may occur, and may leave its impress on the structure 

 of the grain, there is now great reason to believe that, apart from 

 such external influences, the internal phenomena of 

 diffusion may, just as in the typical Liesegang 

 experiment, produce the well-known concentric 

 rings. The spherocrystals of inulin, in like manner, 

 shew, like the " calcospherites " of Harting (Fig. 

 208), a concentric structure which in all hkehhood 

 has had no causative impulse save from within, 

 striation, or concentric lamellation, of the scales and 



otoliths of fishes has been much 

 employed of recent years as a 

 trustworthy and uninistakeable 

 mark of the fish's age. There 

 are 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. 



Fig. 208. 



The 



Fig. 209. Otoliths of Plaice, showing 

 four zones or "age-rings." (After 

 Wallace. ) 



* Cf. Biitschli, Ueber die Herstellung kiinstlicher Starkekorner oder von 

 Spharokrystallen der Starke, Verh. nat.wed. Ver. Heidelberg, \, pp. 457-472, 1896. 

 f Untersuchungen ilber die Starkekorner, Jena, 1905. 



