GH. I.J METAMORPHOSES OF INSECTS. 15 



We will now proceed more minutely to detail the 

 manner in which these transformations are effected, 

 especially the circumstances connected with the es- 

 cape of the butterfly from the chrysalis, continuing 

 to take as examples the three species of butterflies 

 noticed above, and whose caterpillars we have fig- 

 ured in our former volume. There are several pe- 

 culiarities, however, connected with the caterpillar 

 of the swallow-tailed butterfly, which will be con- 

 sidered interesting. 



Until recently this butterfly, which is by far the 

 most remarkable of the British species, was of very 

 rare occurrence in England : but it has within these 

 few years been found plentifully in the fens of Cam- 

 bridgeshire and Huntingdonshire. The caterpillar 

 of this fine butterfly is of a green colour, with vel- 

 vety black rings, which are alternately spotted with 

 red ; it feeds upon various umbelliferous plants, es- 

 pecially the fennel and carrot, preferring the flowers, 

 and is remarkable for having the back of the neck 

 armed with a red-coloured instrument composed of 

 two fleshy horns, branching from a common stem, 

 and shaped somewhat like the letter Y ; this organ 

 appears to be similar in some respects to the horns 

 of snails, and is capable of similar movements, be- 

 ing completely retractile. It appears from the ob- 

 servations of Reaumur that it is only when the cat- 

 erpillar is disturbed that it throws out this instru- 

 ment, sometimes to its whole extent, at others with 

 the horns only protruded thus Y, and occasionally 

 with them unequally extended thus Y ; and, as it 

 secretes an acrid liquor which emits an unpleasant 

 smell, particularly when the animal is irritated, it is 

 probably an organ of defence, to protect it from the 

 attacks of the ichneumon flies. Reaumur mentions 

 the remarkable circumstance that the caterpillar, 

 when spinning the silken cord by which it is to be 

 supported on assuming the chrysalis state, invaria- 

 bly affixes it across its body at the junction of the 



