OF THE MILK-WEED BUTTERFLY. 7 



(rather iudistiuctly ) two-juiuted, the second joint being very small; while in the females 

 there are four tarsal joints, the first quite large, much stouter at the apex, the next two 

 very short, and the fourth or last very minute and indistinct. The first three joints in the 

 female have each two spurs on their inner extremity. The fore tarsi are clawless in both 

 sexes. 



The middle and hind pairs of legs are alike except for the somewhat larger size of the 

 former. The coxal joints are conical, immovably united to the thorax. They are 

 divided into two parts, the coxa and trochantine. The tarsi are five-jointed, all very spiny 

 beneath. The last joint has two long and rather straight claws. 



Abdomen. Nine somites (fig. 1, numbered 1 to 9) are evident in the abdomen of the 

 Lepidoptera. The first is small, forming a sort of neck which is wider than high ; the 

 dorsum is developed into a large bolster, shield-shaped from above, and somewhat over- 

 hanging the base of the second somite. The pleural region presents rather complicated 

 folds, and there is no sternal ossification, leaving a broad membranous surface between the 

 thorax and the sternum of the second abdominal somite. The next three somites increase 

 gradually in height, but each is somewhat shorter than its predecessor. The sternal and 

 dorsal regions are of about equal development. The second sternum shows underneath 

 two shallow furrows, in which tlie knees of the last pair of legs seem to fit. The fifth 

 and sixth somites decrease gradually in size. The last three somites require a different 

 description for the two sexes. In the female the dorsum of the seventh somite is longer 

 than the preceding, and the sternum is produced backwards to a point, and its posterior 

 border emarginated. The eighth tergum is shorter than the seventh, and the whole som- 

 ite much less high ; its flat sternum looks forward, opposing the hollow posterior aspect of 

 the seventh ; thus forming with the latter a wide, cave-like vestibule, in which the orifice 

 of the vagina is situated. The ninth, and last, somite is very small, and in re^DOse, almost 

 wholly retracted within the eighth. Inferiorly and laterally it is produced into two bluntly 

 triangular lobes, or flaps, between which lie the openings of the digestive and reproduc- 

 tive organs. The ninth sternum is reduced to a simple ring, connecting these flaps infe- 

 riorly. 



In the male the seventh somite is simply smaller than the preceding. The eighth, 

 however, is remarkably developed, for its sternum is produced laterally far beyond the 

 tergum forming two flxlse clasps with bifid tips, the inferior tooth being the stouter, and 

 both teeth strongly incurved. The ninth segment resembles that of the female, except in 

 being somewhat larger. To its sternum, however, are articulated the true male claspers, 

 to be described farther on, and between these projects the penis. The anus lies within 

 the flaps above the sexual organs as in the female. 



II. Internal Anatomy. 



From this brief description of the exoskeleton we may pass to the internal anatomy of 

 our butterfly. To best study it, the insects should be hardened for a few days in alcohol, 

 made gradually stronger, and then some specimens should be cut with a razor into lono-i- 

 tudinal halves, which will show the natural position of the internal organs. It is well to draw 

 the razor slightly on one side of the median line, as in this way the first part of the dio-es- 

 tive tract, the nerve chain and the dorsal vessel are left intact. Some preparations should 



