AS AN INDEX OF AGE. 29 



focus the strise of adjacent folia cross each other usually at right angles ; but 

 this is not the case at the periphery, where they cross at very varied angles, 

 sometimes forming vortices in which it is difficult to follow tlie direction of 

 the stria?. 



The inorganic substance of scales consists of corpuscles of carbonate and 

 phosphate of lime scattered in the depths of the folia of the organic funda- 

 mental substance. 



There has been much difference of opinion as to the distribution of these 

 calcareous corpuscles. Mandl maintained that the corpuscles were contained 

 in a special tissue situated above the inferior surface of the scale. Agassiz 

 held that these corpuscles are lodged near the superior and inferior surfaces of 

 the scale. Peters believed that the corpuscles are found on tlie inferior 

 surface of the scale, but never on the superior surface, as Agassiz had main- 

 tained. Williamson made use of sections, and was the first to recognise the 

 presence of corpuscles in the entire thickness of the scale. 



Baudelot agreed with Williamson in the main points, and after an analysis of 

 the scale, layer by layer, enunciated the following more detailed points : — 



" (1) In the most internal folia of scales the corpuscles are few in number or 

 entirely absent. 



" (2) In the folia following the most internal the corpuscles become rapidly 

 very numerous, and their number increases as one proceeds from the internal 

 to the external surface of the scale. 



" (3) Xear the external surface of the scale, the corpuscles are so numerous 

 that they form a sort of compact web in the thickness of the fundamental 

 organic substance. 



" (-i) The external calcareous investment of scales is simply a conglomera- 

 tion of fused calcareous corpuscles." 



In other words, calcification of the folia of scales is more advanced as one 

 approaches the external surface of the scale, and this one can readily under- 

 stand, as it is on the internal surface that the formation of new tissue takes 

 place. In each of the more internal folia of the scale calcification is more 

 pronounced towards the periphery than in the focal region. In the focal 

 region the corpuscles are less numerous, usually isolated and separated from 

 one another by spaces completely deprived of calcareous deposits. Towards 

 the periphery of the folia, on the other hand, the corpuscles are very abundant 

 and become massed together throughout the fundamental substance. In the 

 most external folia of the scale, in which the calcification is much more 

 advanced, the corpuscles are seen to be numerous throughout the entire extent 

 of the folia. 



The corpuscles are not of the same volume at all points of the same lamella. 

 In the focal region they are relatively large ; but as one proceeds from the 

 focus to the periphery they gradually diminish in size until they become of 

 extreme delicacy. The volume of the corpuscles is not the same in the various 

 folia of the scale ; thus in the most recent and internal folia the corpuscles, 

 where they exist, are usually much smaller than in the more external folia. 

 The size of corpuscles seems to vary with the age of tlie scale ; for example, in 



