CABBAGE WHITE BUTTERFLIES 171 



corpuscles may be found sunk in the tissues which 

 they are devouring, and bits of striated muscle, plainly 

 recognisable under the microscope, have been seen 

 buried in the protoplasm of such corpuscles. In the 

 same way the muscles of a Tadpole's tail are eaten 

 up by wandering corpuscles, which carry the sub- 

 stance which they have appropriated into the blood. 

 How they part with it, and how the growing organs 

 get the benefit of the food contained in the corpuscles, 

 are questions to which we can at present give no 

 satisfactory answer. 



What is a pupa ? I have found few, even among 

 professed naturalists, who could give a full and 

 accurate answer. The common notion is, I believe, 

 that the pupa is a resting-stage, during which the 

 imago or winged Insect is formed. The form of the 

 pupa is supposed to be merely protective. Within 

 the hard, usually dark-coloured, and therefore incon- 

 spicuous pupa-skin, the imago is believed to form. 



There is some truth in this, but it is not the whole 

 truth. Wings, legs, antennae, proboscis, and other 

 characteristic members of the imago, form, as we have 

 seen, during the last larval stage. They become free 

 for a short space at the time of pupation, but are then 

 folded against the breast and glued down. The pupa 

 is to external appearance a Moth or Butterfly which 

 has glued down its half-expanded appendages ; it is 

 enveloped in a close-fitting skin, which will be cast 

 when the imago emerges. 



Swammerdam must have often asked : Since the 

 parts of the Butterfly are plainly to be seen within 

 the larval skin, how is it that the Butterfly, complete 



