524 A Preliminary Monograph of the 



The production of such an ideal description would be much 

 facilitated also by improvements in the mechanical accessories 

 of the microscope. There is no reason, for instance, why the 

 simple stage-forceps should not be supplemented by an additional 

 arm, securely attached to the upright portion of the stand which 

 carries the stage, and provided with a fine screw-motion for eleva- 

 tion and depression. This additional arm might easily be pro- 

 vided with a steel spring, holding a square piece of very thin 

 glass, ruled by some one of the delicate dividing-engines, so well 

 known at the present day, to twentieths of a millimetre, in a 

 transverse and a vertical direction, forming squares of the in- 

 dicated dimensions. The movable stage, carrying the forceps 

 which support the mounted specimen, being moved in such a 

 way as to bring the insect under the glass scale, the latter could 

 be depressed, so as to approach very near to the upper surface 

 of the object, and the transparency of the glass would readily 

 admit of any desired measurements. Readings could, by estima- 

 tion, be made to the tenth part of the least division of the scale, 

 or in this case to the .005 part of a millimetre. In the various 

 species of Trogophloeus, the mutual distance of the minute punc- 

 tures, even when unusually dense, could easily be expressed in 

 «uch a unit. In this way the diameter of the punctures, their 

 average mutual distances in various portions of the body, the 

 length of pubescence, length and width of scales, length of the 

 antennae, femora, tibiae, and tarsi, diameters of the eye and of 

 its minute component lenses, length and width of all the major 

 parts of the body, and many other facts, could be recorded in 

 absolute numerical quantities. 



I am far from believing this to be a mere flight of fancy. 

 In describing any animal of large size and higher organization, 

 it would undeniably be considered invocative of criticism if 

 actual measurements of the various parts of the arms and legs, 

 of the hairs, ears, eyes, and other similar facts were not given; 

 and yet in the animals treated of in the present paper, the varia- 

 tion in any part of the body is so much less from individual to 

 individual of the same species, that if such facts could be re- 

 corded, they would be of much greater relative value. 



Regarding the species of large and difficult genera, the ordi- 

 nary description is confessedly inadequate. There is not one of 



