36 THE PERIODIC GROWTH OF SCALES IN GADID^ 



period the minute scales appear as circular discs, which lie adjacent to one 

 another in regular order; but they do not as yet show any special covering. 

 The scales so far lie parallel to the upper surface of the body, and do not 

 project nearly so strongly into the epidermis as they do later; but at the 

 posterior end of each scale tlie epidermis projects inwards, as can be seen in 

 tranverse sections. In the strips of skin intervening between the scales, cells 

 of the dermis lie embedded in great numbers in a ground substance consisting 

 of a few irregularly arranged fibrillse. 



Above the anterior end of the scale several elements penetrate between the 

 basal membrane of the epidermis and the scale, adding themselves to the 

 scleroblasts already present there, and resembling the scleroblasts in their 

 appearance. An increase of the dermis cells internally to the scales also 

 takes place. As the scale was originally enveloped symmetrically on all sides 

 by formative cells, a change in the distribution of scleroblasts is the more 

 noteworthy. On the upper or more external surface of the scale they lie 

 closer to one another than on the lower or more internal surface ; but they lie 

 particularly close to one another at the posterior part of the scale. As the 

 latter portion of the scale is specially active in growth, the highest point of the 

 scale germ becomes displaced entirely in the caudal direction. The slight in- 

 ward invagination of the under surface of the epidermis, continued here from 

 previous stages, becomes gradually considerably enlarged ; Ijut the epidermis 

 by this infolding gains as little as previously any part in scale formation. 

 Contemporaneously all layers of the skin grow in thickness, and the epi- 

 dermis comes thereby to consist of a large number of layers of cells. In the 

 dermis also that part situated between the lamellre and the scales undergoes a 

 great degree of cell proliferation. The scale comes thereby to lie on a layer of 

 loose connective tissue, by which it is separated from the deeper part of the 

 dermis, in which the ground substance had already undergone a lamellar 

 differentiation. At the same time there takes place an increase of dermis cells 

 between the epidermis and the scales, and new elements thus become added to 

 the scleroblasts on the upper surface of the scales, while the uppermost or most 

 external layers of the dermis separate scales and scleroblasts from the epidermis. 

 The scales thus become enveloped on all sides by loose connective tissue, from 

 which the scleroblasts receive new auxiliaries. The posterior end of the scale 

 shows as yet no connective tissue covering. The result of this mode of growth 

 is that the scale always inserts itself deeper in the epidermis. The scales, 

 along with their envelopes of connective tissue, have the appearance of papillae 

 which press the epidermis before them in an oblique direction caudalwards. 

 The epidermis during this process does not become uneven on the external 

 surface, but, on the other hand, is thrown into folds on the internal surface. 

 Klaatsch regards these folds as equivalent to the "epithelial pockets" described 

 by C. Vogt. A section shows the corresponding epidermic processes running 

 out pointed in front and extending far underneath the posterior border of each 

 scale. The position of the scale in the skin now undergoes an imjDortant 

 change. The posterior border of the scale becomes pressed against the upper 

 surface, and the anterior end expanding underneath the epidermic continua- 

 tions, becomes sunk towards the interior. From the original horizontal 

 position the scale passes into a position oblique to the upper surface. The 



