MEANS OF DEFENCE OF INSECTS. 261 



luent of the body, and not at or under its extremity, as 

 obtains in most insects. By means of such a position, 

 the excrement when it issues from the body, instead of 

 being- pushed away and falling, is lifted up above the 

 back in the direction of the head. When entirely 

 clear of the passage, it falls, and is retained, though 

 slightly, by its viscosity. The grub next, by a move- 

 ment of its segments, conducts it from the place where 

 it fell to the vicinity of the head. It effects this by 

 swelling- the segment on which the excrement is depo- 

 sited, and contracting the following- one, so that it ne- 

 cessarily moves that way. Although, when discharged, 

 it has a longitudinal direction, by the same action of 

 the segments the animal contrives to place every grain 

 transversely. Thus, when laid quite bare, it will 

 cover itself in about two hours. There are often 

 many layers of these grains upon the back of the insect, 

 so as to form a coat of greater diameter than its body. 

 When it becomes too heavy and stiff, it is thrown off, 

 and a new one begun". — The larvae of the various spe- 

 cies of the tortoise-beetles (Cassida, L.) have all of 

 them, as far as tliey are known, similar habits, and are 

 furnished besides with a singular apparatus, by means 

 of which they can elevate or drop their stercorarious 

 parasol so as most effectually to shelter or shade them. 

 The instrument by which they effect this is an anal 

 fork, upon wliich th.ey deposit their excrement, and 

 which is sometimes turned up and lies fiat upon their 

 backs ; at others forms different angles, from very 

 acute to very obtuse, with their body; and occasionally 



" Reaum. iii. 220 — Compare Vallisnicri Espcricm. c(l Osservaz. 195. 



Ed. use. 



