2JH PTILOTA : IMAGO EXTERNAL ANATOMY. 



character, since the neuters are entirely destitute of them. 

 They are also entirely wanting to the great mass of Coleoptera 

 (having been only noticed in a few small Brachclytrn, Paussus 

 cruciatus, and some of the Dermestidee), in many hugs and 

 water bugs, and also in many neuropterous insects. That 

 these ocelli are in fact supplemental eyes, appears evident from 

 the experiments of Swammerdam and Reaumur ; the latter 

 of whom varnished the back of the head, covering the ocelli, 

 in more than twenty bees, which he then set at liberty three 

 or four paces from the hive, but not one of them knew 

 where to find it again, nor appeared to search for it. They 

 flew at random to the adjacent plants, but never to a dis- 

 tance ; and though they seemed to have no difficulty in fly- 

 ing, he never saw them rise in the air as those did \\liosc 

 facetted eyes he had varnished over. The internal anato- 

 mical structure of the ocelli also proves that they are dis- 

 tinctly organs of vision, 

 (c) The Antenna (a in the figures). 



We are now to turn our attention to a pair of organs per- 

 haps the most characteristic of the insect tribes. These are 

 two articulated appendages of a most variable character, af- 

 fixed at the sides of the head, and generally between the eyes 

 and the mouth. Although occasionally wanting, and gene- 

 rally rudimental in the preparatory states, these organs are 

 never absent in the imago state. I shall have occasion 

 subsequently to enter into the question of the use of these 

 organs, which have been the subject of much dispute amongst 

 naturalists. It will be sufficient here to notice that they are 

 exceedingly sensitive, and are evidently of the highest degree 

 of sen-ice to the insect. From their great diversity of 

 structure they are employed by entomologists as affording 

 the most satisfactory characters to distinguish the various 

 genera, &c. It will therefore be essential to enter more 

 into detail respecting their peculiarities. I will therefore 



