STRUCTURE OF INSECTS. 7 



The form of the head and of its various organs is exceedingly varied ; 

 the variations of the mouth are of the highest importance, serving for 

 the primary divisions into orders. 



The AntenncB are generally elongated, and consist of a number of 

 rings attached together, but varying in structure, not only in almost 

 every species, but also in the sexes of the same species ; those of the 

 males being often much more complex than those of the females. 

 These organs, from their existence only in insects and other articu- 

 lated animals, as well as from their diversity of structure, have at- 

 tracted much attention, and have been employed as excellent distinc- 

 tive characters of genera, &c. They have received the names of 

 filiform (thread-like), setaceous (bristle-like), moniliform (necklace- 

 shaped), cylindrical, prismatic, ensiform (sword-like), fusiform (spindle- 

 shaped), aristate (terminated by a hair), dentate (toothed), serrated 

 (saw-like), pectinated (comb-shaped), flabellated (fan-like), ramose 

 (branched), furcate (fork-like), geniculated (elbowed), perfoliated 

 (with a knob, composed of loosely attached joints), lamellate (with 

 a plate-like knob), plumose (feathered), verticillate (with whorls of 

 hair), &c., according to their various form and clothing. 



The Composite JEt/es are exceedingly varied in their size; sometimes, 

 as in the male hive bee, nearly occupying the whole surface of the 

 head: they are composed of a number of minute transparent corneous 

 hexagonal facets, representing the cornea, and being more or less 

 gibbous, according to the carnivorous habits of the species. The 

 number of these facets is equally varied ; thus in the ant there are 

 but fifty, whereas in the eyes of the butterfly, according to Geoffroy, 

 there are not fewer than 34,650. From the elaborate anatomical re- 

 searches of Muller and others, it is evident that each of these facets 

 operates as a distinct organ of vision ; and from an interesting me- 

 moir lately presented by Mr. Ashton to the Entomological Society, it 

 appears, that in some species (Libellula) the upper facets are of a 

 larger size than the inferior ; whence a distinct kind of vision may be 

 supposed to be possessed by these different sized facets, according 

 with the habits of the insect. A similar observation was made by 

 Plooke in Tabanus. 



The ^/?;?/>/e£V/es(ocelli)are generally three in number, and arranged 

 in a triangle on the crown of the head ; they are of a simple and 

 semiglobular form. The eyes of larva?, spiders, and some other 

 Annulosa are simple ocelli, arranged in groups. 



B 4 



