498 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1920. 



color (pi. 2, B) . Its thick skin forms a rigid shell except at the articu- 

 lation between the seventh and eighth segments of the abdomen, where 

 the flexible membrane of this joint permits a free rolling motion to 

 the terminal segments, the ninth of which is provided with a strong 

 spine on each side. The. head terminates in a sharp, beak-like point 

 directed downward (pi. 3, F) . In the spring when the moth is ready 

 to emerge from the pupa, the pupa forces itself through the front 

 end of the cocoon, when the moth makes its escape by breaking 

 through the head end of the pupal skin, leaving the latter projecting 

 from the rent in the cocoon (pi. 2, C) . 



We may get an idea of how the pupa makes its exit if we cut a 

 small hole in the rear end of its chamber and push the hard-shelled 

 creature gently forward with some blunt-pointed instrument. As 

 the head is forced under the sloping partition in front of it, the beak 

 penetrates the floor and the pupa gently slips out of the widening rup- 

 ture. (Fig- 9.) A further examination of the partitions shows that, 

 though each consists of a tough disk of felted silk, they are very inse- 

 curely attached to the chamber walls except at their bases, the lower 



edges being but 



_^^^. ii mil M „,, ,,. "^mt^iL^^ ^ loosely stitched or 



^^Cs a-.-^ ^^j^—L-^J^^J ^ scarcely attached at 



=SSS ^^^P all. They thus sug- 



Fig. 0. — Diagram illustrating how the pupa of Bucculatrix o-ggt valves or trap- 

 emerges from its cocoon. (Compare with F on plate 3.) ^ ., ,. 



doors rather than 

 true partition walls, and the above experiment has given us an indi- 

 cation of their function. 



The living pupa has its own propeller at the rear end of its body, 

 consisting of the motile terminal segments and the lateral spines on 

 the ninth. We can imagine that by a semirotary motion of these 

 parts the pupa pushes itself forward, the spines enabling it to obtain 

 a hold on the silk walls of its chamber. As its head comes beneath 

 the sloping surface of the nearest valve-like partition (pi. 3, F, f) the 

 latter gives somewhat, but, as this one crowds against those in front, 

 it exerts an increasing downward pressure on the pupa's head which 

 forces the beak of the latter through the floor of the cocoon. The pupa, 

 continuing to press forward as the rent enlarges, eventually forces 

 half or two-thirds of its body through the opening. (Fig. 9.) The de- 

 sired position being thus obtained, the spines of the quieted propeller 

 probably now serve to anchor the rear end of the body in the cocoon. 



The moth of Bucculatrix (pi. 2, D) is larger than the shield-bearer 

 moth, being about one-seventh of- an inch in length to the tips of the 

 folded wings. The general color is yellowish, mottled with brown, 

 black, and white. The crown of the head is covered with long plumes 

 combed forward over the brow in bangs which almost conceal the 



