THE LARVA. 21 



The legs of larvoe are of two kinds : 



1. Horny and composed of joints ; these we may con- 

 sider as the legs proper, or the true legs. They are the 

 chief instruments of locomotion, are always six in number, 

 attached to the under side of the three first segments of 

 the trunk, and consist usually of the same parts as those 

 of the perfect insect. 



2. Back of the true legs, along the body, many larvEe 

 have little fleshy props, without joints ; these may be called 

 prolegs ; they serve chiefly as props and stays, by which 

 the animal keeps its long body from trailing, or by Avhich 

 it takes hold of surfaces. They vary in form and number 

 from one to as many as eighteen. They may be arranged 

 in two principal groups : 



1st. Those furnished with terminal claws ; and 

 2d. Those without any terminal claws. 



Spiracles. — The breathing organs of larvi?e consist of 

 tubes called spiracles that enter the Ijody from the two 

 sides of the rings or segments. As these are made on 

 the same plan as those of the adult insect, we will omit 

 them until we reach that part of our study. 



Aijpendayes. — While, on the average, larvae have no 

 other organs than those that have already been described, 

 yet on several of them exist curious appendages, such as 

 protuberances, horn-like processes, rays, retractile organs, 

 and the like, which should be considered as extraneous 

 appendages rather than as portions of the regular struc- 

 ture of the body, or of its clothing or covering, and so 

 might demand a separate consideration. 



