8 INSECT TRANSFORMATION 



usually well marked in the divisions of the cuticle. Examining 

 one of the legs, we notice that here again are long tubular 

 pieces of hard chitin, such, for example, as the " thigh " and 

 the " shin," while between them, as at the " knee " joint, are 

 flexible regions, so that the leg can be bent or straightened by 

 means of the contraction of its internally-placed muscles. In 

 these jointed legs (Fig. 6) of an insect we see another character 

 which it shares with a lobster or a spider, a character 

 common to arthropods generally, and indeed giving the name 

 Arthropoda (or " Joint-footed ") to the whole group. The 

 exoskeleton is evidently the feature of an insect to which 

 the student of structure must naturally turn first, for its 

 form and arrangement determine the outward appearance 

 of the creature, and it serves as a general framework for the 

 internal organs of the body. 



Reference has already been made to the segmentation the 

 repetition of similar parts from before backwards which is a 

 marked characteristic of all arthropods. In the body of a 

 grasshopper (Fig. i) it can readily be seen that the segments 

 are grouped in three regions. Foremost is the head carrying 

 a pair of eyes, a pair of feelers, and three pairs of jaws ; the 

 general rule among arthropods is for a segment to bear one pair 

 of limbs or appendages and no more, we conclude therefore 

 that there must be at least four segments in this insect's head. 

 Next comes the thorax (or fore-body), which has three segments, 

 each carrying a pair of legs six legs being the usual number 

 for any insect ; further, the second and third segments of the 

 thorax carry each a pair of wings. Bearing as it does, legs for 

 walking and wings for flight, this region is evidently the 

 centre of the creature's locomotor activities. Behind is the 

 long abdomen (or hind-body) in which ten distinct segments can 

 be recognized, most of these are evidently limbless, but appen- 

 dages or outgrowths concerned with the functions of egg-laying 

 can be seen towards the female's extreme hinder end, and the 

 tenth segment carries a pair of short limbs the " tail-feelers ' 

 (or cerci). 



It is now necessary that the structure of these regions of the 

 body should be studied in some detail. 1 The exoskeleton of 



i A. S. Packard: "A Text-book of Entomology". New York, 1898. 

 L. F. Henneguy : " Les Insectes". Paris, 1904. A. Berlese : " Gli Insetti", 

 Milano, 1909. 



