1873. 79 



vermiform movements of the pupa, tliey strongly resist any direct 

 separating force, and the larva skin will not readily even peel off. The 

 capillary adhesion of a very small area is abundantly sufficient to sus- 

 tain much more than the weight of the pupa. An important element 

 in the case is that the sliding of the skin under the vermiform move- 

 ment of the pupa can only take place when there is ^omQpoint d'appui, 

 which in the earlier stage of the process is afforded by the different 

 segments of the pupa, one, or rather several, so to speak, holding the 

 skin, whilst another slides along it ; but at the stage of the process we 

 are considering, ^mq^o. point (Tappui fails, and no further sliding takes 

 place until one is gained by the attachment of the terminal hooks to 

 the silken boss. The " membi-ane " discovered by Dr. W. Osborne no 

 doubt assists to some extent in the same way (by capillary adhesion), 

 for such a membrane there really is. This membrane is neither more 

 nor less than the linings of the tracheae, which are drawn out at each 

 change of skin, and trail behind over the surface of the pupa, frequently 

 adhering to it by the dampness already mentioned. In many insects 

 these tracheal linings form a conspicuous addition to the cast skin, 

 forming long white threads, as they do not shrivel together in drying 

 as the skin itself does. Whether the intestinal lining affords any 

 assistance in supporting the young pupa, I do not know. 

 Bingliill, Hereford : August, 1878. 



DESTRUCTIVE INSECTS IN THE ISLAND OF ASCENSION. 

 BY R. McLACHLAN, F.R.S., &c. 



This little spot in the middle of the Atlantic is suffering to an 

 alarming extent from the ravages of caterpillars, which threaten to 

 destroy all vegetable produce, a most sei-ious matter, when it is con- 

 sidered how greatly the health of its inhabitants — and especially the 

 prevention of that dire scourge scurvy — depends upon a proper supply 

 of vegetables. 



A nicely preserved collection of the perfect insects (with most of 

 their larvte in spirits) has been forwarded to the Secretaries of the 

 Admiralty, and submitted to me through the authorities at Kew. 



It consists of nine species — two of these butterflies, the others 

 moths of the family Noctiudce. All of them may be suspected of 

 having been introduced with plants, &c. 



The butterflies are the very widely distributed Vanessa cardui and 

 Lyccena hcetica, neither of which can cause much damage ; and a Noctua 

 larva was forwarded in error as pertaining to the Vanessa. 



The most destructive of all is our too-well knov>'n Ayrot is seqcluiH, 



