AS AN INDEX OF AGE. 47 



(3) "This intermediate substance is formed at the expense of the basal 

 elements of the papilla. As to the possibility that the fibrillae of the second 

 layer of the scale may develop themselves at tlie expense of the inter- 

 mediate substance by immediate breaking down into such, without participa- 

 tion of the cells, one can say nothing definite, for the reason that there is no 

 possibility of distinguishing the plasma of the formative cells from the inter- 

 mediate substance itself." 



The reliefs on the surface of scales. Ussow has only studied the formation 

 of these reliefs in cycloid scales. In perfectly developed scales this relief 

 has most frequently tlie form of rolls or cylinders, which cover the entire 

 surface of the scale and run parallel to its border. In sections the rolls 

 generally appear as small elevations of transparent homogeneous material, the 

 appearance of which does not differ from that of the first layer of the scale. 

 One finds a cell on such a roll or often behind it. The question might at 

 once be asked, Where do these cells come from '? Klaatsch says that these cells 

 make their appearance out of the connective tissue of the scale pocket, and 

 that as they penetrate into the intermediate space between the epidermis and 

 the scale (in its upper part which has penetrated into the epidermis) as well 

 as between the lower part of the scale and the pocket, they arrange them- 

 selves on the external surface of the scale in curved rows, and form, 

 always in front of themselves, the substance out of which the rolls are 

 made. Ussow saw such aggregations of cells in his sections, but in distinctly 

 later stages than those figured by Klaatsch, namely when the reliefs at the 

 sides of the scale are already completely formed ; but at the stage when those 

 reliefs occurred for the first time, no such cell aggregations existed. Ussow 

 regards it as very possible that these cells later take part in the formation of 

 the reliefs, l)ut he believes tliat the commencement of their formation arises at 

 the expense of the peripheral elements of the papilla, and that for the 

 following reasons : " Commencing with the stage of a plate of scleroblasts, 

 one finds in all subsequent sections the following formation : at the ends of 

 the scales one observes masses of cells which differ in form and colouring from 

 the scleroblasts of the plate, and are similar rather to the peripheral and basal 

 elements of the papilla ; they are, namely, much smaller tlian the scleroblasts 

 and stain more deeply ; in a word, they are cells which have taken no part 

 in the formation of the scale, as the cells which form the scale change their 

 form and appearance, their nuclei become larger, get a pear-shaped form, and 

 are not so intensively stained. In following stages, tooth-like projections 

 formed of transparent substance become observable at the ends of the jjlate, 

 where the cell-masses were situated ; behind each tooth lies a cell, or more 

 properly only its nucleus, for the plasma has. apparently been spent in the 

 formation of the roll or cylinder which appears as a tooth in transverse 

 section." 



In connection with cycloid scales, Ussow believes that the teeth or small 

 si)ines are not in any true sense comparable to rudimentary forms of the spines 

 of placoid scales either in internal structure or development, but that tliere is 

 merely an external resemblance. He holds that these spines are built of the 

 same substance as that of the entire ujjper substance of the scale, that is to 

 say, according to Ilofer, uf hyalodentin. 



