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IV. — A MetJiod of Dissecting Podura Scales. 



By F. H. Wenham, V.P.E.M.S. 



At the last scientific meeting of the Koyal Microscopical Society, of 

 Dec. 10th, a Podura scale was exhibited by me, of which I have 

 formerly made mention. This was a strongly-marked specimen of 

 Eichard Beck's, presented to me by Dr. Grray. In mounting, the 

 cover had rotated, drawing a portion of the ribs with it. One of 

 the note markings had been carried round half way, like turning 

 the handle of a copying press. The various positions of the twisted 

 ribs were shown with such remarkable distinctness, that no question 

 could be raised of their reality. 



Unfortunately this curious object got smashed during the evening. 

 Both the pair of thin glass disks were starred ; the centre of fracture 

 started just on the scale I wished to preserve, so that it could not 

 be seen. I separated the disks, which contained many large speci- 

 mens, and with a keen-edged scalpel attempted to remove some of 

 them, but found that they adhered to the glass with great tenacity, 

 as if they were glued thereto. There was no alternative but to pass 

 the edge of the blade on the glass at random, and collect the 

 scrapings, which were at once remounted. In these I am rewarded 

 with a fine collection of fragments, some puckered up in ridges, 

 giving a perspective of the ribs — pieces are torn ofi", and others cut 

 clean through. Fig. 1 is an outhne sketch 1800 diameters at the 



side of half a scale cross-cut through obliquely. Fig. 2 is another 

 portion from the middle : both were drawn under a ^V^h.* The cut 

 ends of the ribs stand out over the membrane as plainly as the 

 teeth of a rake, thus giving a curious confirmation of Mr. Joseph 

 Beck's statement, that the projection of the ribs is on the under 



* The outlines in the cuts were traced with the camera lucida. My intention 

 was to send a photograph, but as the mirror of my solar reflector swings from 

 below instead of in tlie axis of the instrument, and the shutter of the dark room 

 faces east and west, I found that I could not get the light central enough early in 

 January with the sun on the meridian. I will avail myself of the earliest oppor- 

 tunity of producing these photographs. 



VOL. XI. Q 



