f>10 PSYCHOLOGICAL PHYSIOLOGY. 



in times of danger. It is remarkable that these organs in all the pre- 

 ceding instances are of a red colour : it might be thence concluded that 

 the substances which they secrete or contain are very rich in acids. 

 The larva of Chn/somela Populi has likewise secreting organs upon its 

 back, in the form of two conical knobs on each segment, whence, at a 

 time of danger, a white, milky, and strongly scented fluid issues, which 

 may also serve chiefly as a means of defence. In the processionary 

 caterpillar, according to a recent discovery of Dr. Nicholai, the whole 

 external surface of the skin secretes a sharp juice, which is distributed 

 over the body in a farinaceous form, and which acts very prejudicially 

 upon all organisms that inspire it ; therefore workmen who are 

 occupied in woods where this caterpillar is numerous sicken very 

 rapidly. Bechstein knew that the processionary caterpillar was pre- 

 judicial to the touch, but he ascribed their effects to the hair that was 

 removed by it. 



Other larvae, which have not received means of defence in such 

 organs of secretion, nor in the thick hairy coat that envelopes them, 

 construct cases for themselves, into which they retire upon the approach 

 of danger. We find such among the larvae of the Coleoptera, namely, 

 in the larva of Clythra, which all dwell in cases formed by themselves, 

 and in which they change into pupse. Among the Lepidoptera, the 

 remarkable genus Psyche forms such cases of morsels of wood, and 

 there change into the pupa, and even the naked apterous female still 

 continues to dwell in it. Besides these, the family of the Phryganea 

 are furnished with this means of defence ; their larvae live in the 

 water, and furm cases of small stones, pieces of wood, shells, c., 

 which they also close with a distinct lid when they change. 



The sting is the chief weapon of offence. The majority of insects 

 furnished with a sting as a means of defence belong to the order of the 

 Hymenoptera ; it is but recently that a stinging lepidopterous insect 

 has been found, and which we have before mentioned. It is always 

 the female which possesses the sting, or else the neuters ; the males 

 never have it. We refer to the anatomical division of this work for its 

 structure, and we can only say of the way in which it is used as a 

 weapon, that the insect upon the approach of clanger projects it from 

 the abdomen, and thereby endeavours to wound its enemy with it. It 

 is not so much the mechanical injury that occasions the pain as the 

 poison which is injected into the wound. There are solitary instances 

 of two or three stings being present at the same time, and which also 



