AS AN INDEX OF AGE. 41 



existing connective tissue of the scale pocket which has become annexed to 

 the scale. In regard to the deeper-situated connective tissue, this questionable 

 layer must be defined as tense connective tissue without cells, whose formative 

 cells probably originated from the connective tissue of the scale pocket. "The 

 development of this peculiar tissue can only be fully understood by taking 

 into consideration phylogenetic factors extending far backwards. Its peculi- 

 arity may, however, be partly explained by reference to the development of 

 the entire dermis. As Hatschek has shown, and as I also find in the trout, 

 the dermis consists originally of a layer, the formative cells of which lie only 

 on the inner side. The formation of the fibrillar structure of the layer is 

 independent of cells, which only arrive later in its interior. The dermis cells 

 return likewise to an embryonic stage in the course of scale formation, and 

 it is conceivable that events which govern the formation of the entire dermis 

 repeat themselves in detail." 



Regarding the relation of the lower to the upper layer, it is of significance 

 that the upper layer exists for a long time alone, and that it is not till later, 

 when the covering of the scale has completed itself, that the other part of the 

 scale first appears. There exists indeed a genetic relationship between both 

 layers, and the external bony layer has indeed occasioned the formation of the 

 second. But now as it is a matter not simply of a connective-tissue lower 

 layer of the original scale, but of an integral portion of the entire structure, it 

 follows that a sharp separation between both layers is as little tenable as a 

 separation between the formative cells of both surfaces. At the margins of the 

 scale the layers cohere intimately with one another. As the lower layer 

 becomes impregnated with calcareous salts, a closer coherency is by that means 

 given to both layers. 



This impregnation with calcareous salts never takes place in the lower layer 

 to the same extent as in the upper layer ; the substance remains little capable 

 of resistance against alkalies ; but Klaatsch believes that a sclerotic-like forma- 

 tion takes place, though in lesser degree. The calcareous concretions which 

 ^landl has described thus appear in the lower layer. They are ovoid, layered 

 bodies which are largest in the centre of the scale. Immediately beneath the 

 outer layer they lie so thick and congregate so intimately together that 

 "Williamson has made a special third layer out of that part. Leydig referred 

 to them as " Kalkkugeln." He overrated their significance in scale formation. 

 "Now they again gain significance, but in another sense to that which the earlier 

 authors thought. These formations appear as the lower scale layer gradually 

 becomes changed by a sclerotic-like formation. The scale represents a plate, 

 which consists of an outer and an inner layer. The outer is bony tissue, the 

 inner owes its origin to connective tissue, ' das in den Sclerosirungsprocess 

 einbezogen worden ist ; sie besteht aus theilweise sclerosirten Eindegewebs- 

 lamellen, zwischen denen keine Zellen liegen.' " 



In a later paper Klaatsch* returns to the question of the development of 

 the teleostean scale, and comes to the conclusion that it follows the same 

 course as that of the bones of the head, which he now describes. He points 

 out that his former work requires correction as regards the origin of the 

 elements which form the scale. The scleroblasts in reality arise from the 



* Klaatsch, 1894. 



