ARTICULATES. 001 



sued channels or veins. The corpuscles have forms like those 

 which are found in animals of the superior grades. The ner- 

 vous system consists of a symmetrical arrangement of nervous 

 threads in two lines, situated on the face of the abdomen, and 

 connected by knots or ganglia, at every ring of the body. 



The mouth of insects, although made up of the same essential 

 parts, has these modified into two principal forms of structure, 

 one of which is adapted to chew, and the other to suck food. 

 The former are named mandibulate, (from Lat. mando, to chew;) 

 the latter, haustellate, (from Lat. haustellum, a sucker.) In the 

 order Hymenoptera, however, biting mandibles are united with 

 sucking jaws. (Plate XV. fig. 12b.) 



But the most striking peculiarities of insects relate to the 

 changes or metamorphoses which they undergo during their stages 

 of growth, corresponding, in some degree, with the developments 

 made in other animals, yet differing from them in being station- 

 ary at certain periods. (Plate XV. fig. 2.) 



By far the largest part are oviparous. The eggs are generally 

 oval, but they are seen in other forms, sometimes round and 

 sometimes cylindrical. Some are smooth and shining; others 

 are beautifully sculptured. They vary as to color, but white 

 and green predominate. 



The Flesh -Fly, Musca carnaria, is ovoviviparous, the eggs 

 being hatched within the body. 



The larva state of insects commences when the egg is con- 

 verted into a footless worm, resembling the higher Entozoa, or 

 the inferior Annelidans, in its organization, and continues until 

 the wings begin to appear. The term larva, (a mask,) was ori- 

 ginally adopted by Linnseus, who regarded insects, while under 

 this form, as masked. It is applicable to the young of all insects. 

 In the Scaly- winged Insects or Butterflies, (Lepidoptera,) and 

 most of the Sheath-winged Insects or Beetles, (Coleoptera,) the 

 larva, at the time of its escape from the egg, has the rudiments 

 of three pair of legs upon the thorax, though these are little 

 more than simple claws, except in the Carnivorous Beetles. The 

 eoft, white larvae of the Beetles are called Grubs; those of certain 

 Flies or Two-winged Insects, (Diptera,) are called Maggots ; 

 those of Butterflies, Moths, and Millers are termed Caterpillars. 

 The young of the HEMIPTERA, including Bugs, Cicada, Plant- 

 Lice, &c. ; and of the ORTHOPTERA, including the True Locusts, 

 Crickets, Cockroaches, &c., do not emerge from the shell until 

 they have a close resemblance to the parents in every thing, 

 excepting wings; and they can hardly be regarded as having 

 the characteristics of real larva. 



