AGRIUS CONVOLVULI. 34? 



the contents of the digestive tract, was well seen on September 14th, 

 when a single one, out of the 15 younger larvae, was found at the 

 end of a shoot, where it had been eating the young yellowish 

 leaves. This larva was of a much paler green than all the others 

 which had been eating the older darker leaves. The caudal horn 

 is not so long as in the larva of 6". ligustri; it tapers very slightly 

 from base to apex, and it is held so as to nearly make a right 

 angle with the line of the back. During this stage, it is characterised 

 by a very slight curve, with the concavity directed anteriorly, 

 conferring upon it a very unusual appearance, for the curve in the 

 horn of other Sphingidae, and in the two last stages of this species, is in 

 the opposite direction. [For the general appearance of the horn see 

 pi. xv., fig. 2 (x 5'8).] The bifidity of the horn varies immensely, 

 and this is probably true of the younger stages of all other Sphingid 

 larvae, although they have not been examined with equal care. 

 These extreme individual differences are to be expected because 

 of the vestigial nature of the part in question. [The larva that 

 hatched on September 7th, possessed the most strongly marked 

 fork: it is shown from the front in pi. xv., fig. 3 (X 5°)-] The 

 terminal bristles are seen to be stout, and each ends in a very 

 slight knob, while the rest of the horn (of which only the upper 

 part is shown in detail in fig. 3) is clothed with thickly crowded 

 minute short hairs, each springing from a tubercular base. The 

 structure is thus very different from that of the next two stages in 

 which the horn presents a thorny appearance, due to the presence of 

 a much smaller number of far larger hairs and tubercles. (Compare 

 pi. xv., figs. 3 and 4, with 9 and 16.) [I am now able to state that the 

 caudal horn of Sphinx ligustri, in the first stage, is similar to that just 

 described, and bears the same relation to the stages which 

 immediately follow.] One of the younger larvae also possessed a 

 deeply-notched horn, but not so pronounced as that represented in 

 fig. 3. The ends of all the horns of other larvae were much like 

 that shown in fig. 4 (X 50), some having a rather deeper notch. The 

 dark colour of the horn slightly suffuses the larval surface around 

 the base of this structure. The well-known tubercles and bristles 

 are distinct from the very first, having the arrangement shown in 

 %• 2 (X 5'8). Each abdominal segment, from the ist-7th, bears 

 five of these prominent structures upon each side, and there are a 

 large number of them upon the indistinctly separated segments 

 posterior to the 7th abdominal. The arrangement upon this part 

 can be seen in figs. 2 and 6, and upon the thoracic segments in figs. 

 2 and 5. There are at first no other shagreen-tubercles * upon the 

 larva, but at the end of the stage, just before the resting-period, 

 there is an indistinct appearance of these structures. A fairly high 

 power only shows that the green larval surface is mottled with white, 

 and does not support the view that tubercles are present. It is 

 probable that the effect is due to the partially-formed shagreen-dots 

 of the next stage, showing through the transparent skin. The head 

 is thinly covered with short hairs (figs. 2 and 5). The subdorsal 

 line is certainly absent at first, but there is no doubt about its 



* Poulton still calls the primary tubercles and their setae shagreen-tubercles 

 (see our criticism antea p. 309, footnote). True shagreen-tubercles are secondary 

 structures. 



