576 LECTURE LIX. 



stead of bones, they have a hard integument or shell. Their mouths are 

 formed on constructions extremely various, but generally very complicated : 

 Fabricius* has made these parts the basis of his classification ; but from 

 their minuteness in most species, the method is, in practice, insuperably 

 inconvenient ; and the only way, in which such characters can be -rendered 

 really useful, is when they are employed in the subdivision of the genera, 

 as determined from more conspicuous distinctions. Insects have most fre- 

 quently jaws, and often several pairs, but they are always so placed as to 

 open laterally or horizontally. Sometimes, instead of jaws, they have a 

 trunk, or proboscis. In general, they pass through four stages of 

 existence, the egg, the larva, or stage of growth, the pupa, or chrysalis, 

 which is usually in a state of torpor or complete inactivity, and the imago, 

 or perfect insect, in its nuptial capacity. After the last change, the insect 

 most frequently takes no food till its death. 



The Linnean orders of insects are the coleoptera, with hard sheaths to 

 their wings, generally called beetles ; the hemiptera, of which the sheaths 

 are of a softer nature, and cross each other, as grasshoppers, bugs, and 

 plant lice ; the lepidoptera, with dusty scales on their wings, as butterflies 

 and moths ; the neuroptera, as the libellula, or dragon fly, the may fly, 

 and other insects with four transparent wings, but without stings ; the 

 hymenoptera, which have stings, either poisonous or not, as bees, wasps, 

 and ichneumons ; the diptera, with two wings, as common flies and gnats, 

 which have halteres, or balancing rods, instead of the second pair of wings ; 

 and lastly the aptera, without any wings, which form the seventh order, 

 comprehending crabs, lobsters, shrimps and prawns, for these are properly 

 insects ; spiders, scorpions, millepeds, centipeds, mites, and monoculi. 

 The monoculus is a genus including the little active insects found in pond 

 water, which are scarcely visible to the naked eye, as well as the Molucca 

 crab, which is the largest of all insects, being sometimes six feet long. 

 Besides these there are several genera of apterous insects which are 

 parasitical, and infest the human race as well as other animals. 



The vermes are the last and lowest of animated beings, yet some of them 

 are not deficient either in magnitude or in beauty. The most natural divi- 

 sions of vermes is into five orders ; the intestina, as earth worms and 

 ascarides, which are distinguished by the want of moveable appendages, or 

 tentacula, from the mollusca ; such as the dew snail, the cuttle fish, the 

 sea anemone, and the hydra, or fresh water polype. The testacea have 

 shells of one or more pieces, and most of them inhabit the sea, and are 

 called shell fish, as the limpet, the periwinkle, the snail, the muscle, the 

 oyster, and the barnacle. The order zoophyta contains corallines, sponges, 

 and other compound animals, united by a common habitation, which has 

 the general appearance of a vegetable, although of animal origin ; each of 

 the little inhabitants, resembling a hydra, or polype, imitating by its 

 extended arms the appearance of an imperfect flower. The last order, 

 infusoria, is scarcely distinguished from the intestina and mollusca by any 

 other character than the minuteness of the individuals belonging to it, and 

 their spontaneous appearance in animal and vegetable infusions, where we 

 * Entomologia Systematica, 6 vols. Hafniae, 1792-8. 



