154 DESCRIPTIONS OF PREPARATIONS. 



the resolution of the fat body. A pupa preserved in alcohol at this stage retains its 

 light colour. One in the possession of Mr. Poulton, has clearly defined though 

 feebly coloured streaks, corresponding to the coloured streaks of the caterpillar. 

 Under natural conditions the pupa hardens and becomes dark-brown. As this 

 change of colour takes place underground, it cannot be due to the action of light. 



Swammerdam was the first to point out that the appendages are readily 

 separable in a newly-formed pupa, or may be dissected out from under the cater- 

 pillar skin when it is ready to be moulted. The operation is easy if the pupa or 

 caterpillar are preserved in alcohol. 



In the caterpillar it will then be found that the angle of the gena already 

 mentioned in the pupa corresponds to the mandible : that the pupal antennae and 

 maxillae are folded upon themselves : that the wings are mere tubercles. All these 

 parts expand and assume their proper position as the caterpillar skin is being cast off. 



It will also be found that the horn-like projection of the pupa consists of a right 

 and left division, one belonging to each maxilla : that its labium consists of two back- 

 wardly turned lobes united basally, and of great size in Pieris : that the coxa of the 

 limbs are united to the thorax, the trochanter inconspicuous : that the femur and 

 tibia are bent at an angle on one another, the former concealed by the latter, and that 

 the joints of the tarsus are not differentiated. Though the -first abdominal spiracle 

 is hidden by the wings, it retains the character of an open functional spiracle. 



If the horn-like projection of Sphinx Ligustri is opened when the moth is 

 nearly ready to emerge, the bases of the antlia of the imago will be found to fill it 

 imperfectly. Each base forms a thick band or ribbon attached anteriorly to the 

 head, lying under the outer surface of the projection, inside which it is folded back 

 once upon itself. It then runs on into the straight median portion of the pupal 

 maxilla. It appears to me likely that it is differentiated from a part, and not the 

 whole of the outer wall of the pupal maxilla, but the histological details of the pro- 

 cess are still wanting. Owing to the fact that the antennae, antliae, &c., of the 

 imago are formed within the corresponding organs of the pupa, and are withdrawn 

 from them leaving them empty when the imago emerges, the pupal organs have 

 been spoken of as ' cases ' or ' thecae,' e. g. Ceratotheca, Glossotheca, &c. But it 

 must be borne in mind that just as the change from caterpillar to pupa takes place 

 by a moult, and the pupal organs are formed within the corresponding organs of the 

 caterpillar, from which they differ essentially in shape and size, so it is with the 

 change from pupa to imago. Indeed there is reason to believe that more than one 

 moult takes place during the pupal stage. In Sphinx Ligustri and in some others (?) 

 a thin pellicle may be raised from the inner surface of the last pupal skin ; and Pro- 

 fessor Westwood has drawn my attention to a passage in Curtis (British Ento- 

 mology, Description of Plate 147), where that author records the fact that an imago 

 of Acherontia Atropos cast off a complete and thin pellicle after emergence from the 

 pupa-skin. The pellicle in question appears to be homologous with the thin skin 

 cast by the sub-imago of Ephemeridae after it has taken flight from the water, having 

 already just emerged from another skin. 



The pupal state of Sphinx Ligustri lasts for forty-two to forty-three weeks. 

 During this period changes take place affecting all the internal organs. Changes in 

 the nervous system continue for the first four weeks, but are then suspended until 

 March. They have been worked out in this moth and in Vanessa Urticae by New- 



