Royal Microscopical Society. ■ 255 



with also pigmentary deposit, in the substance of wMcli the frame- 

 work of the longitudinal ribs is fixed, projecting somewhat on the 

 free surface, and in which the minute cross-bars running between 

 the longitudinal ones at right angles are imbedded, projecting on 

 the surface of the membrane facing the opposite one — the " trans- 

 verse striae" of others (Fig, 6); but besides this, the longitudinal 

 ribs especially, if not the cross-bars, appear to be attached to the 

 opposing surface of the outer or next membrane — if three, by minute 

 more or less wider or narrower vertical projections or septa (Fig, 12) ; 

 so that the ribs are bound to each other by cross-bars, and to the 

 opposite membrane by short columns or attachments at very dif- 

 ferent points ; hence, where these draw the two surfaces of the 

 scale so closely together, that they are virtually in contact, a de- 

 pression at that point occurs in the rib, giving it a lobed, if not 

 twisted appearance, and much increasing the difficulty to separate 

 the membranes from each other, "Where they alternate to either 

 side of the long rib, giving it a furrowed figure, and the scale is 

 illuminated in a particular direction, the rib seems irregularly bent, 

 and on either side, a little to the right or left, we see the illusory 

 appearance of a twin row of beads, caused by the vertical parti- 

 tions or framing at the junctions, refracting the light at those 

 points more than at the adjoining ; whilst a trifling alteration made 

 in the direction of the illuminating pencil divides the rib itself between 

 those rows, and one or two sharp dark shadows start out on either 

 side of the rib, according to focus, and possibly caused by interference 

 (Figs, 23-26), The transverse bars are most likely also slightly 

 attached by their under surfaces to the opposing membrane where 

 we have indications of a beaded character under ordinary observa- 

 tion ; at any rate, the spaces embraced between them are occasion- 

 ally indicated on the opposite surface under some conditions of the 

 incident light (Fig. 5); or they appear capable of being split 

 (Fig, 9). 



In the wavy scales the same parts exist; but instead of the 

 vertical attachments being only close on either side of the long 

 rib alternately right and left, and those of the transverse bars, the 

 attachment takes place also obliquely across the scale, from the 

 quill both sides towards the centre, and maps out the interval be- 

 tween the ribs into rhomboidal areas or beads, according to the 

 illumination, and which are under other positions, &c,, nevertheless 

 seen crossed by the minute transverse bars belonging to the longi- 

 tudinal framing (Figs, 15, 16), 



When the membranes of the scale so attached can be separated, 

 the lines of junction on the opposing surface of the opposite mem- 

 brane are easily seen in some, and give the ordinary appearance of 

 faint yet bright lines, or ribs, or bars, resting on that membrane, 

 at varying angles in relation to the length of the scale (Fig, 7) ; 



