Transactions. id 



species have the bodies comparatively slender, and small in 

 proportion to the wings, which are much larger than those 

 of the Noctuidcv, though not so strong in texture or so 

 robustly veined. Another peculiarity which distinguishes 

 them from the Noctiiidce is that, when in repose (with the 

 exception of a very few that hold their wings erect), like all 

 the butterflies, the wings are horizontally extended, which 

 shows the upper surface of both pairs, while in the Noduidce 

 the fore wings are wrapped over the hinder pair, which they 

 entirely conceal. It is more in the larva state that this 

 order presents the most striking peculiarities. The cater- 

 pillars have only one pair of ventral pro-legs, and that pair 

 the hindermost. This peculiar formation necessitates a 

 curious action in their mode of progression, which is effected 

 by first fixing their six pectoral feet firmly to the substance 

 on which they are standing, and then drawing close up to 

 them the two posterior pairs of feet. When in this position, 

 the intermediate or central segments of the body being 

 raised into a kind of loop, from which they are commonly 

 known by the name of loopers, the hind feet are then held 

 firmly fixed while the body is again fully extended, when the 

 hind feet are again brought up close to them as before, rais- 

 ing the intermediate segments into the loop form as before 

 described. The repetition of this movement gives these 

 singular-looking caterpillars the appearance as if they were 

 carefully measuring the earth, or any other substance over 

 which they may be travelling. It is from this strange mode of 

 walking that they are named Geometro}. They have no legs 

 under the middle part of the body, which necessitates this 

 peculiar mode of progression. Some few of the species have 

 additional pairs of ventral legs, but in almost every case they 

 are very minute ; indeed, I may say, altogether rudimental. 

 I have very frequently been astonished at the great muscular 

 power of some of the Geometrce larva. They can rest 

 entirely on their two pair of hind legs for hours together, 

 with the whole length of the body extended forward in a 

 slanting position. When they are thus resting, some of the 



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