60 



BKITISH BUTTERFLIES. 



thrown back, so that the legs are used as hands to hold it up ; not, 

 however, the claws, but the thick bases of the legs are used, the silk 

 not being on the legs proper, but rather in the incision in front of them. 

 This is the position when the spinneret is at the middle of the girth, 

 but, as the head goes from one side to another, the relation of the 

 parts is much changed, though quite gradually and automatically. 

 .... The girth when completed consists of a number of quite separate 

 threads, showing that each thread is not spun along, and glued to, 

 those that preceded it, and that, therefore, the extremity of the 

 spinneret does not actually reach and touch the previously spun threads 

 which lie deeper in the incision between the segments. . . . The larva 

 moves very leisurely, and with some to-and-fro movement, so that one 

 traverse of the loop takes about three minutes, and the movements of 

 fastening the end of each thread to the twig about one minute, but, 

 between each complete traverse, usually at least one partial journey is 

 taken, i.e., from the twig for about one- third of its length and then 

 back again, and along this piece, especially towards the end of the 

 process, a good deal of local spinning is done, which covers this 

 thicker portion of the loop with an outside building. When the loop 

 is finished, the central third consists of a number of threads more or 

 less separate, or, at least, apparently separate, straight, parallel, and 

 uncomplicated. The end portions are thicker and bound together as one 

 strong strand. . . . In two specimens watched, the whole process took about 



1-| hours in a room at about 64°F After finishing, instead of 



sliding slowly round from the side and bending the head down slowly 

 as it went, to the position it takes when at the central point, it gave it 

 this position at once, so that the head went under the loop somewhat 

 to one side, and, as it then gradually assumed the median position, the 

 thread lay across the middle of the front of the head. At the same 

 time, however, as it assumed the median position, it bent back the 

 head and curved the thoracic segments backwards, so as to bring close 

 together the back of the head and the dorsal thoracic humps; then 

 the thread . became slack over the head and slipped back into its 

 place over the 1st abdominal segment. [The peculiar position in which 

 the girth holds the pupa in Thais is assumed about 24 hours after the 

 pupa is formed.] 



In Papilio machaon the loop consists of a number of quite 

 detached threads, which remain quite distinct and separate to much 

 nearer their attachment. The details of spinning the girth are 

 somewhat different (see op. cit., pp. 213-214), and, when finished, the 

 head is put under the loop, and, after sundry movements, the loop 

 slips backwards between the 2nd and 3rd abdominal segments. 

 Chapman further notes (op. cit., p. 216) that the larva of Pieris rapae 

 makes its girth in a way that is essentially the same as in Papilio 

 machaon, but yet with an amount of variation that renders it actually 

 very different. Essentially the girth is made in front of the larva and 

 between the head and first pair of legs, not between the first and 

 second pair of legs as in Papilio, but the raising of the front segments 

 of the larva, which, in Papilio, may be likened to the " Sphinx " 

 attitude, is in P. rapae carried to an extreme, so that, when the larva 

 is adding to the middle point of the girth, the head is bent back so that 

 the back of the head touches the dorsum, at about the incision between 

 the 2nd and 3rd abdominal segments, the ventral face of head and 



