MICROSCOPIC DRAWING AND ENGRAVING. 



richer and deeper colouring, and all its internal parts acquire 

 their definite forms and tints, as exhibited in the drawing. 



A curious circumstance attends the observation of this insect ; 

 so rapid is its locomotion, that it torments the eye while attempting 

 to delineate it, presenting alternately b its head and tail to the 

 observer. This it effects by bending itself laterally into a circular 

 form, and suddenly whisking round in the opposite direction to 

 that in which it had just bent itself. 



Many species of this genus of insects are, in their perfect state, 

 possessed of a sheathed proboscis, containing instruments with 

 which they are enabled to pierce the skin of men and cattle, 

 injecting at the same time an acrimonious fluid into the wound. 

 The species we are now describing, however, has not been 

 examined minutely enough to determine the form of these organs. 

 It is of a light straw colour, and has two beautiful antennee, or 

 feelers. 



The wings also of this gnat are of a delicate straw colour, and 

 make very beautiful objects when mounted under thin glass in 

 sliders. Some species have wings marginated, and covered with 

 fine scales. These, as well as the feathers on the edges, are good 

 objects for the microscope, and exhibit five or six longitudinal 

 lines on each, which are so strongly marked as to be seen with 

 any kind of light, and do not require superior penetration in the 

 instrument to show them. 



These insects generate while hovering in the air, and the female 

 lays her eggs in the water, selecting an unfrequented spot, where 

 she may deposit them free from danger. This is probably the 

 cause why this larva is discovered with so much difficulty ; the 

 collector being seldom able to procure it two seasons consecutively 

 in the same place. 



59. The method of executing these drawings, practised by 

 Dr. Goring, differed in nothing from that by which an artist 

 makes a portrait, the eye guiding the pencil, and the accuracy of 

 the resemblance depending altogether upon the skill of the artist. 



60. Dr. Goring considered that in such cases the great security 

 for precision offered by the camera-lucida, was not available, 

 owing to the constant mobility of the object delineated; this 

 objection, however, is only applicable to living objects, and 

 that admirable instrument is accordingly used to a great extent 

 in the production of microscopic drawings. As we shall describe 

 it in a future Tract, and explain its mode of application 

 to the microscope, it will not be necessary here to give that 

 exposition. It will be sufficient to observe that a practised 

 draughtsman is capable of giving, not only the general outline, 

 but most of the less minute details of a microscopic object, by a 



