STATES OF INSECTS. 153 



larvae, is the organ employed by them to carry the excre- 

 ment ; with which, instead of letting it fall to the ground, 

 they form a kind of umbrella to shelter and probably con- 

 ceal them. All the tortoise-beetles (Cassida L.) have in- 

 struments for this purpose, as well as an Indian genus 

 {Imatidium Latr.) very nearly related to them. This in- 

 strument is a kind of fork, half as long as the body, con- 

 sisting of two branches, growing gradually smaller from 

 the base to the summit, where they terminate in a very 

 fine point, of a substance rather horny, and attached to 

 the body near the anal orifice. They are armed on the 

 outside with short spines, from the base for about a third 

 of their length. When this fork, as it usually is, is laid 

 parallel to the back, with its points towards the head, the 

 anal aperture points the same way. When the animal 

 walks, the fork points the other way, and is in the same 

 line with the body, and the anus assumes a prone posi- 

 tion a . 



The larvae of a genus of flies (Volucella GeofFr.) re- 

 markable for inhabiting the nests of humble bees, are di- 

 stinguished on their upper side by six long, diverging, 

 pointed, membranous radii ; placed in a semicircle round 

 the anus b : what the particular use of these organs may 

 be, has not been conjectured. Another in my collection 

 has only four upper radii, but below the anus are two 

 fleshy filiform tentacula. One of a Tipulidan described 

 by Reaumur, has also four upper teeth; but instead of 

 two subanal tentacula, has six c . The singular larva of 

 another of this tribe (Chironomm plumosus) has on the 



a De Geer v. 170- t. v.f. 19—23. Compare Reaum. iii. 235—. 

 b Plate XIX. Fig. 11, a. De Geer vi. 137. Reaum. iv. 482. 

 c Reaum. iv. t. xiv./. 9, 10. 



