120 MICROSCOPIC OBJECTS. 



"^ Hints on the Nature of the Markings on the Scales from 

 the Podura plumbea and Pieris Brassica. 



" In the foregoing account of the different scales from 

 the wings and bodies of insects, the design has been to 

 describe their appearance under microscopes, without in 

 the least determining their actual structure. When it is 

 considered that these lines are less than one twenty- 

 thousandth of an inch distant, it must be allowed there is 

 some difficulty in accurately determining their con- 

 struction. 



" The Morpho Menelaus and Lepisma saccharina are of 

 sufficient size to enable us distinctly to perceive that they 

 are composed of two delicate tissues with longitudinal 

 cords (probably tubular) disposed between them ; but in 

 the two delicate ones, the subject of these remarks, we 

 perceive other systems of hnes disposed obliquely ; and as 

 they are extremely delicate, it becomes. a question whether 

 they actually exist, or whether they are appearances pro- 

 duced under certain modifications of the illumination. As 

 there is only one set shown at a time, and I have never 

 been able to see them in a decided way, I have been 

 induced to consider them as appearances only, and not 

 real lines. To determine this point it became necessary 

 to ascertain the cause which would produce such an 

 effect ; and it immediately occurred to me that these 

 obhque lines were occasioned by the disposition and 

 pressure of the superambient scales, in the same manner 

 as the watering or wavy appearance communicated to 



