December, '16] WATSON; VELVET-BEAN CATERPILLAR 523 



on the petioles and stems. The egg is nearly 2 mm. in diameter and 

 somewhat less in height, and flattened on its lower surface. It is 

 prominently ribbed and white until about a day before hatching, when 

 it turns a delicate pink. During August and September it hatches in 

 about three days. Those laid in November required a week or more 

 and often failed to hatch at all. 



The Caterpillar. — The newly hatched larva makes its first meal 

 of the shell of the egg from which it has just emerged, leaving only that 

 portion which is attached to the leaf. It then begins to strip the leaf 

 of the lower epidermis and mesophyll. This is continued until near 

 the end of the second instar when the caterpillar begins to skeletonize 

 the leaf, eating all of the soft material but leaving the veins intact. 

 After the second instar the caterpillar consumes the whole leaf with 

 the possible exception of the midrib and larger veins. Larval develop- 

 ment requires from three to four weeks in summer. There are usually 

 SIX instars, but late in the season a few individuals moulted seven times. 



The caterpillars are extremely variable in color and markings, 

 especially after the second instar. At this time the majority show 

 prominent dark-colored longitudinal lines and narrower ones of white, 

 yellow, or pink, on a ground color of dark green. On many these 

 longitudinal lines are dim or even entirely lacking. These individuals 

 are usually a light yellowish green but some are mahogany brown. 

 Only the more usual dark-colored forms are described in the following 

 paragraphs. 



First Instar (PI. 39, fig. 1). — The newly hatched caterpillar is about 2.5 mm. long 

 and grows to be from 6 to 7 mm. before molting. The head is light brown in color, 

 rounded, bilobed; mouth shining; eyes black. The body is of a uniform light green 

 color without any trace of longitudinal stripes. The tubercles are black and con- 

 spicuou.s; seta? also black. The prolegs on abdominal segments 3 and 4 are 

 about equal in size but are much smaller than those on segments 5 and 6 and are not 

 used for walking. A glance at the prolegs is the most ready means of distinguishing 

 the first and second instars. The legs are light brownish yellow. 



The caterpillar spends about two days in this instar, the average of 

 twenty-seven individuals being 1.7 days. 



Second Instar. — The markings are now very similar to those of the next instar 

 but are somewhat less pronounced. The most conspicuous longitudinal mark is the 

 black border to the lateral line. The papilla; are black as in the first instar but there 

 is aroimd the base of each a light-colored ring. The first pair of abdominal prolegs, 

 as in the first instar, is less than a fourth as long as the third, weak, and not used in 

 walking or clinging; but the second pair is about half as long as the third. These, too, 

 are ordinarily not used in walking but occasionally ai'e so used. 



The larva spends three or four days in this instar (average 3.6 days) 

 and grows to a length of about 9 mm. 



Third Instar. — Head rather square in outline, strongly bilobed, yellowish; ocelli 

 black; mouth dark brown. Body cylindrical; all prolegs used for walking but the 



