19G [September, 



AN INSTANCE OF A DOUBLE PUPAL SKIN. 

 BY T. A. CHAPMAX, M.D., F.Z.S. 



(Plate IV.) 



The specimen, the occurrence of which I report, is of Pier is 

 hrassicae. 



I was ])re paring examples of the terminal segments of pupae to 

 place on microscopic slides, and it is much to be regretted that, in 

 regard to the sample in question, I removed the sixth abdominal and 

 following segments and put them to macerate and soften, hut rejected 

 the remainder, and this was no longer discoverable when I found it to 

 be a very desirable object. M.j observations therefore refer onlj"^ to these 

 last five abdominal segments. 



The specimen was a full pupa, not an empty pupa-skin, and Avhen 

 softened I proceeded to remove the interior from the pupa-skin, but was 

 very much astonished to find that in doing so I removed also an interior 

 skin that had all the characters of a p\ipa-skin. The pupa-skin, in fact, 

 contained not the imago simply but the imago enclosed in an interior or 

 second pupal skin. 



I placed botli these on a slide, and the Plate shows photographs of 

 them. I appear to have placed one of them with the outer and one Avith 

 the inner face upwards, so that the photographs show them reversed. 

 I have, however, placed them on the Plate so as to be easily comparable. 

 They are opened out and laid flat on the slide, the incision just below 

 the spiracles on one side was, of course, made in both by the same opera- 

 tion. I have ])laced on the figures a d to mark the medio-dorsal line and 

 a V to mark the ventral line. It will be noticed that the inner skin is 

 smaller than the outer ; this would naturally be so, but it is so mucli 

 smaller that I think its less mature tissues have shrunk under the action 

 of alcohol and benzole. This probability seems the greater when we see 

 that this inner skin has very satisfactorily flattened out, being fairh^ soft 

 and pliable, whilst the outer one has been more refractory and got folded 

 in consequence, as it happens in tlie region of the genital and anal 

 structures — these can, however, be seen to be ordinarily developed, though 

 now distorted. 



The outer skin is that of an ordinary (female) pupa of P. hrassicae, 

 with dorsal ridge, various black markings, the usual pen-shaped extremity' 

 with cremastral hooks. The eighth abdominal spiracle, tliough obsolete, 

 is very distinct, and the intersegmental membi-ane is seen to be full, 

 laterally, between the sixth and seventh segments, where movement is 

 possible in the living pupa. 



