254: Transactions. 



the colour gets much lighter, the whole body assuming a light yellowish- 

 green tint. Prior to moulting the new head can be seen occupying the 

 space between the old head and the prothorax, which space is thereby greatly 

 extended. The eyes are plain, and the tubercles and hairs on the new skiu 

 can also be seen. The mouth parts of the new head are covered by the old 

 mask. At intervals the fore part of the body lifts slightly, as though the 

 larva were trying to stretch itself. Later these motions become more fre- 

 quent, and the whole fore part of the body is allowed to hang some distance 

 from the leaf; evidently the muscular effort that before held it straight 

 with the rest of the body has been relaxed. The stretching movements 

 become convulsive, the head meanwhile being thrown from side to side. 

 At last the rear segments appear to swell slightly, the ones in front remaining 

 in their former state ; then each segment in turn, from the last abdominal 

 to the first thoracic, is slightly inflated, the whole appearing as an undula- 

 tory movement towards the head as if the inner body were gliding within 

 the old skin ; having reached the head, the motion begins anew at the anal 

 end and proceeds as before towards the head. Several times this pumping- 

 like action occurs, each new motion commencing on the completion of the 

 previous one, and after each the segments gain in size. Then shortly these 

 motions follow with shorter intervals between, till with one supreme effort 

 the old skin is parted round the neck and the new body appears to be forced 

 out of the old skin segment by segment ; in reality the old skin is being forced 

 back. When the prolegs are reached the larva helps free itself by pulling 

 forward. The larva, now free of its old skin, still retains the mask covering 

 the mouth parts ; this it rids itself of by rubbing against the leaf, and then, 

 that accomplished, curls itself up to rest. Almost invariably the freshly 

 emerged larva will consume its discarded skin. In the last two or three 

 stadiums the larva spins a light carpet of silk on the surface of the leaf 

 previous to moulting, in order to securely attach the prolegs during 

 the operation of casting its skin. From the time the larva takes up its 

 position previous to moulting till some hours after the moult, the whole 

 period extending sometimes into two or three days, it takes nothing to 

 eat ; it is on account of this, and the total removal of all undigested food 

 from the alimentary system, that it becomes so much lighter in colour 

 at these periods. An interesting point connected with the feeding of 

 these larvae is that they can change from one food plant to another — 

 for instance, specimens under observation which had been fed up till the 

 4th stadium on S. nigrum, took readily to dahlia, salvia, and potato ; and 

 vice versa. Temperature and other climatic conditions have a great deal 

 to do with extending or shortening the duration of the stadiums. A cold 

 spell may greatly lengthen them, or even increase the number of stadiums 

 beyond the normal, and also has the effect of dwarfing the larvae ; such 

 larvae may hybernate through the winter months. 



Recapitulation. 



1st stadium: Body green; head black ; spiracles circular. 2nd stadium : 

 Body and head green ; clypeus black-margined. 3rd stadium : Double 

 white subdorsal stripe appears. 4th stadium : Spiracles oval. 5th sta- 

 dium : Triple subdorsal stripe ; tubercles ii in segments 2 to 10 (abdominals) 

 inclusive white ; vi white in abdominals 3 to 9 inclusive. 6th stadium : 

 Black margin to clypeus missing ; tubercles on abdominals white, except- 

 ing iii. 7th stadium : Extra moulter ; tubercles all white. 



