8 Transactions of the 



them and the cover for some minutes after they were surronndetl 

 by the cement ; and the appearances which this gave until the air- 

 bubble became disentangled from the scale, and floated away as a 

 globe, were carefully watched. One drawing gives the aspect of 

 the surface of the scale accurately focussed, showing the corruga- 

 tions very distinctly in the huhble ]iOiiion, and the granular bodies 

 are roughly indicated in that portion immersed in the cement, to 

 which I have referred as " Pigment." The other, representing the 

 result of a little deeper focussing, gave a rather better image of the 

 aforesaid pigment granules, while the beaded appearances which I 

 look upon as spurious jrat in a strong claim to notice in the bubble- 

 position. Strange to say too, these were in alternate longitudinal 

 rows of greenish-yellow and blue, a phenomenon, however, with 

 which my object-glass (Merz ^V) may have to do, since it always 

 gives a good deal of colour. 



To exemplify what I take to be hemispherical embossings of the 

 membrane, one of the modifications of corrugations which is exceed- 

 ingly common, I bring forward the scale of the inland Petrobius 

 found by Dr. Gray at Dolgelly this summer. The scale is much 

 like the finer scales from its marine relative, but perhaps shows the 

 embossings a little better than these do generally. I do not think 

 the insect has been found before, and its scale is certainly new 

 to microscopists.* 



This variety of corrugation, which may be likened to embossing, 

 is the nearest approach that I can find to real beads in scales, and 

 as it is exceedingly common it can be easily examined. The dots 

 are wonderfully distinct on the dark scales of Urania Leilus^ and 

 Euploea Midamus and many others, and if the slide is mounted so 

 that a drop of water can be introduced under the cover while the 

 scale is in view, much assistance is rendered to the investigator. 



I would here take the opportunity to allude to the glimpses of 

 the mode of development or plan of structure which is displayed in 

 immature scales. The suggestion was made to me some time ago 

 by Mr. Lowne, but the difficulty of its investigation almost put a 

 stop to further researches on my part, though its force was appa- 

 rent to me at once. Where then shall we look for materials to 

 study ? I think we have on any slide of Podura scales the very 

 materials to hand. Everybody knows that slides of Podura scales 

 contain vast numbers that are too small and too difficult of resolu- 

 tion to examine with satisfaction, and so we all move these out of 

 the field in order to bring the largest only under view, and we look 

 at these time after time, and express our puzzled opinions as to the 

 structure in terms which need only to be compared with each other 

 to show there is a great want of harmony in them. 



* Tlic scales of Macrotoma (Poduridaj) are also excellent examples, 

 t See Figure on Plate LXIX. 



