«J4 On the Spherules which compose the Ribs of the Scales 



searching among the scales, and rotating them with the axis 

 towards the light, I was rewarded with the appearance between 

 the second, third, and fourth spaces at the round end of a large 

 scale, of two rows of beads of a red colour taking directions exactly 

 radiating from the quill. 



At first the ribs are bluish, the obliquely radiating rows of 

 beads are reddish, and much more numerous than the upper parallel 

 ribs, which show also a beaded structure. More fortunate resolu- 

 tion shows the reddish beads of the radiating class intervened with 

 whitish, which are best seen at the sides of the scale when the 

 radiating ribs cross the parallel at about an angle of 35°. In this 

 position about jive beads can be counted crossing between the upper 

 parallel ribs. As before, those scales are the easiest to resolve 

 Avhich lie adherent to the cover. Those with a film of air between 

 require a different correction for spherical observation. 



In some cases a good definition shows black ribs and bright 

 radiating ribs of the same size, with red interspaces. At this 

 degree of fine definition the edging of the scale at the round end 

 is a clean black line, and the ribs project slightly, like black points. 



2. A eye-piece ; Powell and Lealand's ^th dry; same illumina- 

 tion. Upper ribs show very small and clear, shaded with two black 

 lines very sharp. At the places where the lower radiations cross 

 them, the black lines are obliterated, so as to give a peculiar shaded 

 twisted appearance, alternating with blue and red shading. On 

 rotating the scale so that its axis forms an angle of 15° with the 

 light, the lower radiating ribs, where they cross the upper at an 

 angle of 40°, also show black hues precisely similar to the others ; 

 both sets of shadows, of a sharp, clear, decisive character, being- 

 seen at once, forming an elegant black lattice-work, the red beaded 

 rib below colouring the upper ribs at the | 'arts where they intersect. 



A very fine phenomenon is exhibited of the effect of the ribs 

 crossing obliquely, which appears to me a perfectly satisfactory 

 proof of the nature of the structure, viz. obliteration of the black 

 line double shadows of both sets of ribbing at the places of intersec- 

 tion; also the colours of the lower ribs glistening there through 

 the upper at graduated intervals, just as are seen when a fine 

 colourless rod of glass is obliquely crossed upon a pink one ; still 

 more so w 7 hen a series of such rods are crossed in radiating positions. 



I have the more pleasure in describing this interesting scale, 

 because this resolution demonstrates the very great advance in 

 microscopic definition since the time Avhen the ribs of the scale 

 were described as translucent and merely an appearance of a dot 

 at the intersection of the lines, whereas there are scores of beads 

 between the ribs in a very small space. At the same time, I may be 

 excused for making a few animadversions on the subject of spurious 

 beads and ghost beads of which so much has lately been said. 



