25 



to the nervures. One begins by trying to crack the pupa along 

 the sutural lines, as between the wings and antennae, but the result 

 is almost always partial or even complete failure ; they can obviously 

 only be fractured correctly by a uniform expansive pressure from 

 within. This pressure may be aided by muscular movement, but 

 its main source is from inflation ; it certainly is not derived from the 

 moth leaving the terminal segments of the pupa and pushing forward 

 to the head end, as would be the case were the process parallel with 

 that by which the larva casts its skin. 



Another use of this expansion by inflation of the imago within 

 the Lepidopterous pupa is to obtain an end-to-end pressure within 

 the cocoon, in order to make an opening of exit. 



In the great mass of Pupje Incompletfe the pupa is provided with 

 a beak with which to assist the opening of the puparium, whether 

 by forcing off a lid, separating the sides of a valvular opening, 

 piercing a slighter place in the cocoon, or otherwise. In nearly all 

 these cases the force which the beak uses against the cocoon is not 

 directly derived from inflation ; the force used is muscular, and the 

 fulcrum from which it acts is the armature of spines on the abdo- 

 minal segment which catch on the walls of the cocoon. 



There are, however, some exceptions. In Eriocrania {piirpure/Ia, 

 etc.) the work of piercing the cocoon is not performed by a beak, but 

 by great jaws. These are very powerful, but are not moved at all 

 by muscles attached to them in the ordinary way, as they have none. 

 They appear to be moved by variations of fluid-pressure against 

 their bases, and, whilst this is guided and varied by muscular action, 

 its actual source seems to be the result of inflation. Again, in the 

 Limacodids the pup?e are very soft, and the spines arming the abdo- 

 minal segments are often small and weak. Their use seems to be 

 confined to extruding the pupa from the cocoon after it has been 

 ruptured. 



The cocoons are always very short, round, and squat, and have a 

 peculiar brittle texture, so that end-to-end pressure from within, or, 

 indeed, various other pressures tending to distort the cocoon, result 

 in a lid being broken off one or other end. This lid is usually fairly 

 circular and regular, but it is irregular in the sense that the rupture 

 marking it out may occur anywhere within rather wide limits, and is 

 due to general brittleness and not to the preparation of a special 

 suture or valve. This is seen if a needle be used to a sound cocoon 

 to break off a lid. The lid breaks off easily, starting from the point 

 where the needle presses, which could not, of course, always happen 

 to be exactly on a specially prepared line ; nay, further, it breaks off 

 as easily at the wrong as at the right end of the cocoon. It is not 

 xjf course always, but very often is, as round and regular as that 

 broken off by the emerging moth. The end-to-end pressure from 

 within is obtained by the expansion of the moth within the pupa 

 case by inflation. That the lid shall form at the right end and with 

 ii minimum of tension is determined by the pupa being furnished 



