168 THE VILLI AND BEADING DISCOVERED 



Manipulation. — I have long known that the apparent thickness 

 of the black margins of cyHnders and spherules depends upon 

 two factors — angular aperture of the objective and of the illumi- 

 nator. 



The outlines are seen thinnest with a wide-angled condenser, 

 such as Abbe's, and seen very thick by a low-angled one, such as 

 a one-and-a-half-inch Ross's objective. Objectives of many kinds 

 have been successfully employed as condensers for many years ; 

 also an Iris diaphragm and Powell's stops. In practice, a touch 

 of the hand rapidly reveals the best apertures for superb 

 definition. 



Battledore scales require magnificent glasses to display the 

 beading on their surfaces. But very ordinary ones show the well- 

 known circular dot ; better ones descry pillars with oddly-shaped 

 bases connected internally by filaments, and if the focal depth be 

 sufficiently delicate, single pillars, which indeed are huge villi, 

 may be traced within, downward from head to base. To show 

 what can be done by the best modern glasses, the other day, 

 examining the Battledores of Polyonunatus Bceticus, tlie quill or 

 stem was seen glittering with the most minute, diamond-like 

 beading, evidently intended to secure the quill safely in its place, 

 the wing pocket.* I have seen this in no other species. 



The types of villi lately discovered are in themselves highly 

 interesting : — Batonettes, Venniforms, Confluents, and lofty Erectilcs. 

 Besides these, eight other kinds had been previously discovered : — 

 Beaded Villi, Embossed Villi, Ciliated Villi, Connected Villi, Banana 

 or hunched Villi, Spinous Villi, Tall Villi. There can be no doubt 

 that many other varieties exist, and perhaps, after another seven 

 years' search, new kinds may be discovered. By the permission 

 of the Editor, a few of these will be represented I)y drawings. 

 Mr. Watkins, King's Mill House, Painswick, supplies a list and 

 wings. 



* I extract an entry from my catalogues : — 

 " Supplied by Mr. Curties, scales {a, l>, c, d, e). Nearly all the scales show 

 ribs and Villi downwards, but scale [a] shows the other surface beautifully 

 jewelled with beading, especially the quill. When the ribs are shown upwards, 

 the bosses appear and are prolonged inwards. A i-32nd was used at last to 

 differentiate the two membranes (Feb. 8th, iSSi.) I reckon this minute 

 beading at i- 150,000th of an inch in diameter." 



