No. l6.] INSECTS OF CONNECTICUT. 2^ 



and best-known group represented by crabs and lobsters have ten 

 legs ; but in the lower and less familiar groups the number of legs 

 varies. 



EXTERNAL STRUCTURE OF INSECTS. 



Generally speaking, all mature insects are covered with a 

 hardened exoskeleton formed of chitin. This serves for the 

 attachment of the muscles and for the protection of the vital 

 organs. The trunk is divided into three more or less distinct 

 regions; viz., head, thorax, and abdomen. Immature insects do 

 not always show these divisions. 



Head. 



The head bears the eyes, the mouth-parts, and the antennae or 

 feelers. The eyes of adult insects are usually compound; that 

 is, made up of a large number of simple eyes placed close to- 

 gether, each having the form of a hexagon, and the whole 

 resembling a piece of honeycomb. The simple eyes that go 

 to form the compound eye are known as facets, and vary from 

 about fifty in the eyes of certain ants, to nearly a thousand, 

 as is the case with "butterflies and dragon-flies. In addition to 

 the compound eyes there are isolated simple eyes, called ocelli, 

 often placed on the front of the head between the compound 



eyes. 



A pair of jointed antennae, usually situated between and in 

 front of the compound eyes, serve as organs of touch. The an- 

 tennae vary greatly in size and shape in the different kinds of 

 insects, some having antennae which are filiform, some clavate, 

 some feathery, etc. The antennae of the sexes often differ, those 

 of the male usually being more prominent. 



The mouth-parts are fitted either for biting or for sucking. 

 Biting mouth-parts consist of an upper lip (labrum) and an 

 under lip (labium), between which are two pairs of jaws that 

 move horizontally. The upper jaws are called mandibles, and 

 are for tearing off the food; the lower jaws are known as 

 maxillae, and bear jointed appendages called maxillary palpi. 

 The labium is furnished with jointed appendages called labial 

 palpi. 



Sucking mouth-parts consist of a jointed tube or proboscis 



