15 



(eomposition) of the scale; we shall see later that on the contrary they are piates, 

 which staud out in very obvious relief on the surface of a continuous, fibrous 

 plate which forms the substratum of the scale. 



»To obtain a clear impression of the structure of the skeleton, we must 

 study it under a magnification of 100 — 400 diameters. Placing a scale under 

 the microscope and examining each of its surfaces, it is easy to determine that 

 the two surfaces have a characteristic and quite different appearance. ■ — The inner 

 surface is corapletely smooth; tiie outer on the other haud is covered with round 

 calcareous piates resembling small medallions, which stand up very distinctly from 

 the fibrous grouud-substance of the scale. The number of these piates ou a scale 

 of 2 mm. in length is at least one thousaud.« 



B. then examiues the two surfaces separately beginning with the outer. 

 He first studies the medalliou-like piates. He finds that they vary greatly in form 

 and considers that »we can scarcely say more in general thau that they show 

 rounded contours; some are circular,- most have the form of a more or less elon- 

 gated ellipse, which is sometimes irregular. « After briefly describing several of 

 these forms B. euquires what these plate like bodies really are and writes: »Each 

 plate may in regard to its thickness be considered as a sort of very flat cylinder 

 with two parallel eud-surfaces, an inner which is counected with the fibrous ground- 

 substance of the scale, and an outer which projects freely. The height of the 

 cylinder (or thickness of the plate) is ca. 4 to 6 hundredthparts of a millimeter. 

 The outer end surface has a plain, quite flat surface definitely bouuded as to its 

 circumference, which makes each plate resemble a small lookingglass surrounded 

 by a frame of dark colour. The faet that this outer end-surface allows the light 

 to pass through it and throw a lightreflexion ou the fibrous ground-substance of 

 the scale has given rise to a pecuhar optic illusion; as I have already mentioned, 

 il has beeu taken by several observers to be holes bored in the structure of 

 the scale. 



»The inner end-surface of the plate rests ou the fibrous groundsubstauce of 

 the scale and is fused with it. It is a little broader than the outer, and whereas 

 the latter shows a gently rounded contour, this in the former is usually more 

 irregular with more or less distinct halls of calcareous substance in its length. 

 Sometimes the inner end-surface is broadened and expanded into a fine lamella 

 with indented contours ou tlie underlying ground-substance.« 



B. next describes the foliate structure of these cyUnders and continues with 

 a detailed account of how the}^ are arranged on the surface of the scale. — »The 

 calcareous piates do not touch one auother; between them is a larger or smaller 

 interspace in which is seen the fibrous structure of the scale. 



»Taken as a whole, the piates are arranged in rows which are more or 

 less regular and parallel to the margin of the scale. In each row their lougest 

 diameter follows the longitudinal axis of the row itself. Not all rows traverse the 

 whole surface of the scale; some disappear after a louger or shorter course and 

 seem to lose themselves amongst the adjacent rows, as can be easily settled by 

 counting the rows along and across a scale; in the first direction there are more 

 than in the latter.« 



