PHYSIOLOGY OF INSECTS. 127 



(plantula) arises from between the claws, and this 

 joint is furnished with two other claws. 



463. The under surface of the joints of the 

 tarsus are very frequently covered with soft 

 cushions (pulvilli) ; these are composed of an 

 almost infinite number of minute hairs, which, 

 at their ends, are slightly dilated, and constantly 

 exude an adhesive gummy matter. 



464. By means of these gummy pulvilli, insects 

 possessing them are enabled to walk freely on 

 smooth surfaces, even with their backs downwards^ 

 against the power of gravity : other insects whose 

 pulvilli exude a somewhat oily matter, run with 

 ease and safety on the surface of water. 



465. 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 

 (pulvinulus) : this is a part of some importance 

 for distinguishing characters. 



466. There are attached to the telum, or last 

 segment of the abdomen, many very singular ap- 

 pendages ; the uses of some of these are known, 

 of others unknown. 



467. The appendages of which the uses are 

 ascertained are these, the sting (aculeus\ as in 

 bees ; the external ovipositor (ovipositor exertus), 

 as in the ichneumon ; the tubular retractile ovi- 

 positor (tubulus\ as in the bot-fly ; the saw 

 (terebella), with which female insects bore a hole 

 to deposit their eggs. 



