140 EVENINGS AT THE MICKOSCOPE. 



ous ; for it requires species of different sizes and differ- 

 ent constructions. M. Sprengel found that not only- 

 are insects indispensable in fructifying different species 

 of Iris, but some of them, as I. XipTiium, require the 

 agency of the larger humble-bees, which alone are 

 strong enough to force their way beneath the style-flag ; 

 and hence, as these insects are not so common as many 

 others, this Iris is often barren, or bears imperfect 

 seeds." * 



The legs and feet of Caterpillars are constructed on 

 a Tery different plan from those of perfect insects, as 

 you may see in this living Silkworm. The first three 

 segments of the body, reckoning from the head, are 

 furnished each with a pair of short curved limbs set 

 close together on the under side. These represent the 

 true legs of the future moth, and show, notwithstanding 

 their shortness, four distinct joints, of which the last is 

 a little pointed horny claw. The whole limb resembles 

 a short stout hook. The two segments occur which are 

 quite smooth beneath, and destitute of limbs ; and then 

 on the sixth we begin to find another series, which goes 

 on regularly, a pair on each segment, to the eleventh 

 and final one, with the single exception of the tenth 

 segment, which is again deprived of limbs. 



But these organs are of a very peculiar character. 

 They have no representatives in the mature insect, but 

 disappear with the larva state, and they are not con- 

 sidered limbs-proper at all, but mere accessory develop- 

 ments of the skin to serve a special purpose. They are 

 sometimes called clasp ers, sometimes false-legs, but 

 more commonly pro-legs. 



Each consists of a fleshy wart, which is capable to 

 * Penny Cyclop., art. Bee. 



