38 THE PERIODIC GROWTH OF SCALES IN GADID^E 



of conceutric ridges. It remains uncovered for a considerable time, until it 

 also becomes overlaid by the posterior border of the next anterior adjacent 

 formations. 



Structure of teleostean scales from the Tiistogenetic standjwiyit. The dermis 

 cells which take part in scale formation are large elements with well-developed 

 nuclei, each of which shows a distinct nuclear membrane, and also, as a rule, 

 a large nucleolus. These cells lie at first so close to one another that they 

 mutually affect one another in shape. From a circular form they pass over 

 into a polygonal one. While the cells on the internal surface of the scale 

 become disconnected from one another on the first separation of scale sub- 

 stance, different cell layers come into formation on the external surface. 

 Above the deepest scleroblasts immediately overlying the young scale a 

 layer of cells extends which easily allows itself to be lifted up in co7itinno. 

 At the margins of the scale the original condition persists, as here the cells of 

 the outer as Avell as the inner surface unite themselves into an almost complete 

 covering for the scale substance. 



The superficial scleroblast layer presents a very characteristic structure. 

 Its polygonal-shaped elements simulate a fiat epithelium. Between the 

 protoplasmic parts, which stain deeply in carmine or hematoxylin, there 

 exists a network which does not stain. This network appears like a system 

 of intercellular spaces, and there is nothing so far to prove that the clear 

 strips between the cells are an intercellular substance. The further changes 

 of these cells clear up the meaning of the intervening substance. The 

 cells undergo a process of change which seems to take place for all in a 

 similar manner. Each cell extends itself in one direction, which is not quite 

 determined in relation to the entire scale. It attains thereby a lengthened 

 form, and the nucleus comes to have a more peripheral situation in the cell. 

 The nuclei of adjoining cells during this process come to lie nearer one 

 another. In all the cells a part containing the nucleus becomes distinct 

 from a part in which there is no nucleus. In the latter part the protoplasm 

 loses at one place its power of taking on stains, and in this part there 

 appears a clear circular spot which resembles a nucleus in size and general 

 form. There is no internal structure in this clear spot, which afterwards 

 expands in the direction of that part of the cell farthest from the nucleus, 

 and finally unites with the clear network between the cells. 



The different stages correspond with a process of cell-metamori)hosis : the 

 clear strips between the cells, owe their origin like the clear spots in the cells 

 above described, to a substance which has become differentiated from the rest 

 of the protoplasm. 



This substance unites with that part of the scale already existing. The 

 nucleus and a part of the protoplasm are preserved. The substance derived 

 from the cells is thus a secretory product. Klaatsch says, "An dem 

 vorliegenden Objekte, welches fiir die Untersuchung des scleroblastischen 

 Processes in Flachonbilde sich vortrefllich eignet, konnte ich nichts wahr- 

 nehmen, was zu Gunsten der Annahme sphiche, dass Zellen i}i ioto in 

 das Produkt aufgingen ; die Kerne zeigten keine Veriinderung, ich sehe 

 daher in der Bildung der Hartsubstanz einen Abscheidungsprocess." 

 This product, the substance of the scale, is thus an intercellular substance 



