140 EVENINGS AT THE MICEOSCOPE. 



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

 ent constructions. M. Sprengel found that not only 

 are insects indispensable in fructifying diflferent species 

 of Iris^ but some of tliem, as I. Xiphium^ 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 very different plan from those of perfect insects, as 

 you may see in this living Silkworm. Tlie first three 

 segments of the body, reckoning from the head, are 

 furnished each with a pair of short cuiwed 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 wq begin to find another series, which goes 

 on regularly, a ]iair on each segment, to the eleventh 

 and final one, with the single exception of the tenth 

 segment, which is again dej)rived of limbs. 



But these organs ai-e 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 sj)ecial purpose. They are 

 sometimes called claspers, sometimes false-legs, but 

 more commonly pro-legs. 



Each consists of a fleshy wart, winch is capable to 



* Penny Cyclop., art. Bee. 



