7s [September, 



ON THE PUPATION OP THE NYMPHALID^. 

 BT T. A. CHAPMAN, M.D. 



From my earliest entomological experience, tliis subject, as an 

 engineering problem, had a great attraction for me, and it was not long 

 before I had succeeded in observing the whole pi^ocess, by which the 

 pupa, soft, and apparently helpless, gets hold of the tuft of silk which 

 is to support it, not by getting through the end of the caterpillar skin, 

 but by withdrawing the tail from the effete skin and passing it up be- 

 hind it. Few years, until this one, have passed in which I have not 

 repeated the observations, which possess an unfailing interest. It so 

 happens, also, that some years ago I interested myself in the question 

 as to the normal number and arrangement of the spiracles of insects, 

 and as to how the various number of spiracles that occur are to be 

 explained by the suppression of some and the varying position of 

 others. Among the observations then made were some on the changes 

 in the number and positions of the spiracles during metamorphosis. 

 The j)upation of the Vanessidi w^as not omitted in these observations, 

 and yielded an item bearing on the " membrane " obsei'ved by Dr. AV. 

 Osborne. It is perhaps, therefore, fitting that I should state the 

 result of my observations as the subject has been brought up for 

 discussion. 



It is to be noted that the process of casting a skin, whether by 

 larva or pupa, is a process of vermiform creeping, i. e., creej)ing with- 

 out the aid of legs ; the segments of the insect are soft and worm-like, 

 but under powerful muscular control, notwithstanding their softness 

 and the delicacy of their tegument. In the fresh pupa of Vanessa, for 

 example, the segments are rounded with deep folds betw^een, and not 

 smoothed down, hard and telescoped as in the mature pupa. As the 

 casting of the larva skin becomes nearly completed, the thoracic portion 

 of the skin still covers the ventral aspect of the abdominal segments, 

 whilst already the dorsal slit in the skin has passed so far backwards 

 as to allow the removal of the terminal segment with its hooks. 



At this critical point it is obvious, as the result of my observations, 

 that the good old explanation of how the pupa is sustained, is largely 

 true, that it is suspended by the folds of the larva skin being grasped 

 in the intervals of the segments of the pupa. But there is another 

 and at least as important an element in the case that has not, I think, 

 been mentioned, and that is, that the interior of the larva skin and the 

 surface of the pupa are damp or actually wet, so that by capillary 

 attraction and atmospheric pressure they adhere w'ith considerable 

 firmness, and whilst they will gradually slide off each other by the 



