848 



1 NS 



inched from the head and cleaned, the lenses are 

 found to be as clear as crystal. Reaumur fitted one 

 of them thus removed to a lens and found that he 

 was able to see through it distinctly, the object being, 

 however, greatly magnified. Ordinarily the eyes are 

 entire, but sometimes the antennae are inserted so 

 close to their inner margin that the eyes are thrown 

 out of their ordinary form, and more or less surround 

 the base of the antennae. Sometimes even the eye is 

 thus completely divided into two parts by the antenna; 

 being inserted in the middle. The same thing occurs 

 in both respects, when the lateral margins of the head 

 become acute, in which case they enter the anterior 

 limb of the eye, and either partially, as in Dorcus, or 

 entirely, divide it in two parts ; thus forming an upper 

 and an under eye : hence these insects may be said 

 to have four composite eyes, which in fact appears to 

 be the case in the whirl wig-beetles (Gyriniu), and in 

 the males of some May-flies (Ephemera). 



Fig*. 63, Head of Coptocephalos ; 64, ditto of Tetraopes; 65, 

 ditto of Dorcas ; 66, ditto of Ephemera biomlata. 



Ordinarily the eyes are sessile, that is, attacned by 

 by their entire breadth to the head ; but in some 

 instances they are placed at the extremity of foot- 

 stalks formed of a continuation of the corneous 

 covering of the head, and consequently incapable of 

 separate motion. This is especially the case in the 

 dipterous genera, Achias, Diapsis (fig. 60), Plagioce- 

 phala, and others, in some of which the footstalks are 

 nearly as long as the entire body ; the same occurs 

 in some species of strepsipterous insects, as well as in 

 some exotic bugs (Heteroptera). Again, the eyes of 

 insects are generally either almost flat, or but very little 

 elevated above the surface of the head (fig. 53) ; but 

 in many cases they are almost globose and very pro- 

 minent (fig. 54), a peculiarity respecting which, and 

 connected with their habits, has been noticed by the 

 late celebrated Swedish entomologist Dalman, who 

 observes that the very prominent eyes of insects 

 generally indicate their habitation to be either in 

 sandy situations or upon the margins of water ; this 

 is exemplified in the coleopterous genera, Cicindela, 

 E/aphrus, Omophron, and Sterna, and in the hemi- 

 pterous genera, Salda and Alydtis. Moreover, insects 

 with prominent eyes seem to be especially rapacious 

 in their habits, as in the genera above mentioned, 

 Lit>i/Jn/ti, Hemerobius, &c. 



In many dipterous insects a remarkable diversity 

 exists in the size of the eves in the two sexes, those 

 of the males being very large, and united upon the 

 crown of the head, whereas those of the females are 

 much smaller, leaving a space between them upon 

 the top of the head (figs. 67 and 68). The same also 

 occurs in the male hive-bee. 



In some insects, however, the eye appears to be 

 completely wanting ; this is asserted to be the case in 

 the remarkable parasitic insect, thence named Braubi 

 txrca, m the eenus of beetles, Climdium, Kirby ; and 



ECT. 



in the ants forming the genus Ponera. In like man- 

 ner we have been unable to observe the least trace ot 

 eggs in more than one exotic species of ant ; and in 

 some of the Centipedes the same is stated to be the 

 case. 



Figs. 67, Head of male ; 68, ditto of female Syrphus. 



b. The Ocelli or Simple eyes (o in the figures). 

 These organs (sometimes also named Stemmata) are 



minute nearly globular lenses placed upon the crown 

 of the head or the forshead, between the upper region 

 of the eyes. Unlike .ie composite eyes, they are 

 often entirely wanting, and are never present in the 

 image unless as accompaniments to the latter. In 

 their organisation they appear to be similar to the lateral 

 point-like eyes of caterpillars or the eyes of spiders. In 

 general they are three in number, placed in a tri- 

 angle, or more rarely almost in a line. Occasionally, 

 however, there are but a pair of these ocelli, as in 

 many lepidopterous insects, where they are present, 

 although concealed by hairs, in the mole-cricket, in 

 many bugs and smaller frog-hoppers (Cercopidfs) ; in 

 some of the sand-wasps (Larra, &c.) the hinder pair 

 are almost obsolete ; and in some of the coleopterous 

 insects, belonging to the family Denncstidce, there 

 appears to be but a single ocellus. They appear in 

 the ants to be connected with the development ot 

 the sexual character, since the neuters i j entirely 

 destitute of them. They are also entirely wanting to 

 the great mass of Coleoptera (having been only noticed 

 in a few small Brachelytra, Paussus cruciatus, and 

 some of the Dermestidte), in many bugs 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 riot 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 

 distance ; and though they seemed to have no diffi- 

 culty in flying, he never saw them rise in the air as 

 those did whose facetted eyes he had varnished over. 

 The internal anatomical structure of the ocelli also 

 proves that they are distinctly organs of vision. 



c. The Antennae (a in the figures). 



We are now to turn our attention to a pair of 

 organs perhaps the most characteristic of the insect 

 tribes. These are two articulated appendages of a 

 most variable character, affixed at the sides of the 

 head, and generally between the eyes and the mouth. 

 Although occasionally wanting, and generally rudi- 

 mental in the preparatory states, these organs are 

 never absent in the imago state. We shall have occa- 

 sion subsequently to enter into the question of the use 

 of these organs, which have been the subject ot much 

 dispute amongst naturalists. It will be sufficient here 



