316 Mr. Poulton's notes in 1886 



absorption of radiant energy by larvae. It would be 

 well to test the theory by interposing a transparent 

 athermanous screen between the larvae and the source 

 of light. 



14. The movements of lakvje guided by an appre- 

 ciation OF THE FORCE OF GRAVITATION. — The following 



observation seems to admit of no escape from the con- 

 clusion that larvae are guided by this sense, which must 

 be of great importance to them when they have been 

 blown off their food-plants, or have fallen after being 

 disturbed. During the past summer I had great oppor- 

 tunities of observing the larvae of Vanessa urticce. It 

 was necessary, for some experiments which I was then 

 conducting, that the larvae of the different companies 

 should be kept apart, and accordingly they were placed 

 in separate boxes. But a large company contains from 

 100 to 200 individuals, and it was found exceedingly 

 difficult to put the last larvae in the box without losing 

 or injuring many others which had been previously 

 captured, and which crawled up the side of the box and 

 endeavoured to escape when the lid was removed. The 

 explanation suggested in the title of this section then 

 occurred to me, and I at once tested it by turning the 

 box upside down in my pocket, when the larvae immedi- 

 ately crowded to the bottom of the box, which was then 

 uppermost. On another occasion I witnessed the 

 practical use of this sense of direction in the case of 

 the same species. While the individuals of a large 

 company were being removed from a nettle-bed, about a 

 dozen larvae fell to the ground and escaped among the 

 crowded leaves. Eeturning in the course of half an 

 hour all the larvae were found upon the tops of the 

 nettles, having evidently commenced to reascend without 

 any loss of time. Another instance of the same sense 

 of direction is seen in the behaviour of larvae (such as 

 Pygara bucephala) which have been blown off trees in 

 the neighbourhood of walls and houses, for under such 

 circumstances the larvae obey the instinct to crawl 

 upwards upon any adjacent surface, whatever it may 

 happen to be, and they may often be seen patiently 

 ascending some object which does not lead to their 

 food-plant. But under natural conditions the larvae are 

 not equally liable to be misled by this sense of direction, 



