THE BIOLOGY OF THE ALDER FLEA-BEETLE. 269 



in prominence, but in all specimens which the writer has exam 

 ined, it has been plainly in evidence. 



Emergence of the adult. The pupa is as deeply pigmented 

 as it will ever be about 12 hours before the emergence of the 

 adult. The coloration has already been described on page 266. 



About half an hour before the emergence, the mouth-parts 

 are moved continually. The pupal cuticula first splits along the 

 mid-dorsal line of the mesothorax; then this crack extends back- 

 ward down the mid-dorsal line of the metathorax, and forward 

 along that of the pro thorax. This split is made by the scutellum, 

 which is moved up and down until the cuticula is ruptured. With- 

 in 20 or 30 minutes after the crack has appeared, the head and 

 mouth-parts, as well as the whole pronotum, have been freed 

 from the pupal cuticula. The elytra and wings, which have 

 increased to their full length, have been pushed nearly dorsad. 

 The prothoracic legs project out on each side, strongly bent at 

 the femoro-tibial joint; the mesothoracic legs extend straight 

 down the body, as do also the metathoracic pair, which have 

 been drawn from under the elytra. The antennae lie straight 

 down the middle of the ventral aspect, slightly bent in at their 

 tpis, but entirely free from the legs. The abdominal muscles 

 contract and expand rhythmically. 



After the mouth parts have been freed, the beetles usually 

 rest about 5 minutes, but soon recommence the task of molting. 

 The next step is to withdraw one of the prothoracic legs from 

 its pupal sheath, the other following almost immediately. At 

 this point the antennae usually are drawn out : the head is inclined 

 ventrally as far as possible, and then is suddenly thrown back- 

 ward dorsally as far as is possible, and thus the antennae are 

 pulled out of their pupal cases. Kicking and pushing with the 

 tibio-tarsal joints of the front legs, the beetle rapidly succeeds 

 in drawing out the mesothoracic legs and then the metathoracic 

 legs from their pupal sheaths. The movements of the abdomen 

 have pushed the pupal cuticula farther and farther caudad on 

 the dorsal aspect of the body, and on the wings and elytra, so 

 that by this time they are two-thirds free from the cuticula. The 

 wings and elytra lie entirely dorsad. The pupal skin is now 

 pushed downward and backward off the tip of the abdomen ; the 

 tibio-tarsal joints of all of the legs are used in this process which 

 requires only a short time for its accomplishment. 



