158 Transactions of the 



Dr. Pigott's estimate zuhro^^ to is o^oooth of an inch as inaccurate. 

 I suppose goooo^h to ^^j^o^tli of an inch will come much nearer the 

 actual truth. I have carefully measured small portions of the ribbing 

 and counted the number of bead-like swellings between the hmits. 

 As the beads, if they may so be called, are in actual contact, in fact, 

 are continuous with each other, no allowance can be made for 

 imaginary interspaces. Dr. Pigott himself gives the elements for 

 correcting his estimate where he says, " The spines usually drawn " 

 (i. e. the exclamation marks) " really embrace in general three or four 

 beads." Now, bearing in mind that these beads are in contact, it is 

 only necessary to measure the length of the exclamation marks on 

 the finest Lepidocyrtus scale and divide the measure by four, to see 

 that such a figure as the rsoWoth of an inch is altogether out of 

 the question. 



What then is the true structure of the Podura scale ? I am not 

 disposed to enter into any elaborate discussion on this vexed point. 

 Whatever the ultimate decision shall be, we are all under many 

 obhgations to Dr. Pigott for teaching us that with the improved 

 immersion objective a new series of phenomena can be observed which 

 had hitherto escaped attention. The true interpretation of these 

 phenomena lies perhaps still in the future, and probably reasonable 

 results are most hkely to be attained by such investigations as have 

 been set on foot by Messrs. Mclntire and Maddox.* 



My object at the present time is simply to record in a tangible 

 form by photography, the actual phenomena as I am able to observe 

 them, in the hope that if improved objectives or other modifications 

 in the mode of observation should enable others to obtain more 

 satisfactory views, mine will at least answer the purpose of en- 

 couraging these more fortunate microscopists to record their results 

 in the same manner, and thus to expose them fairly for the instruc- 

 tion and honest criticism of their fellow-labourers. 



Nevertheless, I do not hesitate to say that so far as I have been 

 able to arrive at any judgment I am disposed provisionally to agree 

 in the main with one of the possibihties advanced by Dr. Maddox.f 

 I suppose the scale to be composed of two coiTugated membranes, 

 each thrown into wavy longitudinal corrugations or ribs, and these 

 again crossed by transverse markings, which make the longitudinal 

 ribs appear varicose (or beaded). I suppose the varicose ribs of the 

 two opposite membranes which compose the scale to cross each other 

 at a small angle. In the proper position of the objective, the upper 

 series of varicose ribs comes into focus, while the lower ones are 

 imperfectly seen out of focus. By depressing the objective shghtly 

 the lower ones come into focus, while the upper ones appear out of 

 focus. By depressing it still further the true ribbings are lost sight 

 of, and the exclamation marks, which I am disposed to think with 

 * • Monthly Microscopical Journal,' vol. v., p. 31. t I''-, vol. iv., p. 53, Fig. 3. 



