266 Transactions. — Zoology. 



" The butterflies hibernate, though whether any but the impregnated 

 females survive until the milk-weeds commence to grow, is not definitely 

 ascertained. They commence depositing eggs in the latitude of St. Louis 

 during the fore part of May. Some of the earliest developed butterflies 

 from these eggs begin to apx^ear about the middle of June, and others 

 continue to appear for several weeks. These lay eggs again, and the butter- 

 flies abound a second time in October. Thus there are two broods each 

 year, and though the first brood of larvae are hatched more uniformly and 

 within a more limited time than the second, the two broods yet connect by 

 late individuals of the first and early individuals of the second, and the 

 caterpillars may be found at almost any time from May to October, but are 

 especially abundant during late summer and early fall. 



" The egg is invariably deposited on the under side of a leaf, and is conical 

 and delicately reticulate with longitudinal ribs, and fine transverse strife. 

 It is yellowish when first deposited, but becomes grey as the embryo within 

 developes. 



" In about five days after deposition the egg hatches, and the young 

 larva as soon as hatched usually turns round and devours its egg-shell ; a 

 custom very prevalent with young caterpillars. At this stage it differs 

 considerably from the mature larva ; it is perfectly cylindrical, about 0-12 

 inch long and much of a thickness throughout. The head is jet-black and 

 polished ; the colour of the body is pale greenish-white, with the anterior 

 and posterior horns showing as mere black conical points, and with two 

 transverse-oval black warts, nearer together, on the first joint. It is 

 covered with minute black bristles, arising from still more minute warts, 

 six on the back, and placed four in a row on the anterior portion, and one 

 each side on the posterior portion of each joint ; and three on each side, one 

 in the middle of the joint, and two which are substigmatal, posteriorly. 

 There is a sub-triangular black spot on the anal flap, the legs are alternately 

 black and white, and the stigmata are made plainly visible by a pale shade 

 surrounding them. 



" When the young worm is three or four days old, a dusky band appears 

 across the middle of each joint, and by the fifth or sixth day it spins a 

 carpet of silk upon the leaf, and prepares for its first moult. After the first 

 moult the anterior horns are as long as the thoracic legs, the posterior ones 

 being somewhat shorter ; the characteristic black stripes show quite 

 distinctly, but the white and yellow stripes more faintly. After this it 

 undergoes but slight change in appearance, except that the colours become 

 brighter and that at each successive moult the horns become relatively 

 longer. There are but three moults, and the intervals between them are 

 short, as the worms frequently acquire then- full growth vdthin three weeks 

 from hatching. 



