OF SURFACE. 171 



run with ease and safety on the surface of water, but, if 

 forced beneath the surface, their pulvilli are such admi- 

 rable repellants of wet, that they enable and compel the 

 insect to rise to the surface as soon as the depressing power 

 is removed : beetles inhabiting the water are provided with 

 an oily down, more especially to be observed in the region 

 of the breathing apertures, which effectually prevents the 

 entrance of water. At the end of the^ ungula, between 

 the claws, there is in the locust, and some other insects, a 

 small soft ball called the little cushion or pulvinulus : this 

 is a part of some importance for distinguishing characters. 



There are attached to the telum, or last segment of the 

 abdomen, many very singular appendages; the uses of 

 some of these are known, of others unknown. The appen- 

 dages of which the uses are ascertained are these, the 

 sting or aculeus, as in bees ; the external ovipositor or 

 ovipositor exertus, as in the Ichneumon ; the tubular re- 

 tractile ovipositor or tubulus, as in the bot-fly; and the 

 saw or terebella, with which female insects bore a hole to 

 deposit their eggs. The appendages, of which the uses 

 are unknown or doubtful, are the leaflets or foliol<e ; pin- 

 cers or forceps, as in the earwig ; and tails or caudce and 

 caudula, as in the cockroach and cricket. 



It may be proper to observe, that insects have many 

 external parts here undescribed, and many yet unnamed ; 

 but sufficient are now noticed to enable a reader to describe 

 any insect he may meet with, or to understand any descrip- 

 tion he may read. 



Of Surface. Although this chapter has extended to an 

 unusual length, the description of the skeleton will scarcely 

 be complete without detailing those characters of its sur- 

 face, by which vast numbers of species are readily and 

 almost instantaneously distinguished from each other. The 

 variations in surface are of two [kinds, form of surface, 



