16 STRUCTURE OF INSECTS. 



26. The leg is divided into four parts ; the coara, the femur 01 

 vbigh, the tibia or leg, and tarsus or foot. The coxa (hip or 

 haunch), which may be said to be set into the thorax, is formed 

 of two pieces, and varies much in form. The femur (thigh, m, 

 jig. 3) constitutes the second articulation of the leg; it is always 

 tolerably long, and is sometimes remarkable for its development. 

 The tibia (\eg,jig. 3, n) is next to the femur, which it ordinarily 

 equals in length ; the whole extremity is terminated by the tarsus 

 (o), which is almost always formed of from two to five articula- 

 tions, and frequently bears at the end, one or more hooks or 

 nails. 



" In the generality of terrestrial insects, tfie last segment of the tarsus or 

 foot is provided with a pair of strong horny hooks, which are avaiiarje for 

 many purposes, being used either for creeping upon a moderately rough 

 surface, for climbing or clinging to various substances. 



" Such simple hooks, however, would not always serve. In the case of 

 the louse (pediculus), for example, that is destined to climb slender and 

 polished hairs, such prehensile organs would be of little use. The structure 

 of the foot is therefore modified ; the tarsus in this insect terminates in a 

 single movable claw, which bends back upon a tooth-like process derived 

 from the tibia, and thus forms a pair of forceps fitted to grasp the stem of 

 the hair and secure a firm hold. 



" Many insects, especially those of the dip'terovs order, are able to ascend 

 the smoothest perpendicular planes, or even to run with facility, suspended 

 by their feet, in an inverted position, along substances which, from their 

 polished surfaces, could afford no hold to any apparatus of forceps or hook- 

 lets. In the common flies (Muscida) the exercise of this faculty is of such 

 every-day occurrence, that, wonderful as it is, it scarcely attracts the atten- 

 tion of ordinary observers. The foot of the house-fly, nevertheless, is a very 

 curious piece of mechanism ; for in addition to the recurved hooks possess. 

 ed by other climbing species, it is furnished with a pair of minute membra- 

 nous flaps, which, under a good microscope, are seen to be covered with 

 innumerable hairs of the utmost delicacy : these flaps, or suckers, as they 

 might be termed, adhere to any plane surface with sufficient tenacity to 

 support the whole weight of the fly, and thus confer upon it a power of 

 progression denied to insects of ordinary construction. 



* Another mode of progression common among insects is by leaping, to 

 which from their extraordinary muscular power they are admirably adapted. 

 The common flea, for example, will leap two hundred times its own length. 



" The muscular system of insects has always excited the wonder and 

 astonishment of the naturalist, in whatever point of view he examines this 

 part of their economy, whether he considers the perfection of their move- 

 ments, tne inconceivable minuteness of the parts moved, or the strength, 

 persistence, or velocity of their contractions. Insects are proverbially of 

 small comparative dimensions * minims of nature' 



that wave their limber fans 



For wings, and smallest lineaments exact, 

 In all the liveries deck'd of summer's pride ;' 



their presence, indeed, around us, is only remarked as conferring additional 

 Jfe and gayety to the landscape ; and except when, by some inordinate 



26. How is the leg divided ? What is the coxa ? What is the femur ? 

 What is the tibia ? What is the tarsus ? 



