METAZOA INSECTA. 471 



Nymphalidae or brush footed butterflies, A typical form 

 of each of the large orders of insects so far described has 

 been given, and now one of the Nymphalidae is chosen 

 to represent the order of Lepidoptera. The milkweed 

 butterfly, Danais plexippus Linn. (Nos. 1206-1208) com- 

 bines many of the essential characters of the order. Its 

 egg (PI. 1206, fig. i), like that of many Lepidoptera, is 

 symmetrical and highly ornamented. The caterpillar 

 (No. 1207 ; PI. 1206, fig. 2) has the cylindrical segmented 

 body of most young Lepidoptera. Even in its earliest 

 stage it has this secondary or caterpillar form, the primi- 

 tive Thysanuriform larval stage being wholly skipped. 

 In its biting mouth parts, however, the caterpillar resem- 

 bles the generalized insects. The three pairs are present, 

 the mandibles (PL 1206, fig. 3, md) being strong and 

 well developed. Attached to the second pair of maxillae 

 is the horny tube, the spinneret (fig. 3, j), by means of 

 which the insect spins the silken attachment that suspends 

 the chrysalis. 



The thorax bears the three pairs of jointed legs, each 

 ending in a hook. It has also been found that the meso- 

 thorax and metathorax of the caterpillar bear the rudi- 

 ments of wings beneath the outer skin. These are in- 

 dicated, according to Gonin, 1 by a bagging inward of 

 the hypodermis (PL 1202, fig. i, Pieris brassicae, before 

 the first moult). These rudiments develop as shown by 

 fig. 2, which is the wing-rudiment of the full-grown larva 

 with its trachea and branches. By dissecting away the 

 body wall just before pupation, the crumpled wings may 

 be seen as in fig. 3. The existence of these appendages 

 in the larva demonstrates more forcibly than almost any 

 other discovery possibly could, a fact difficult- for most 

 people to grasp fully ; namely, that the caterpillar is a 

 young butterfly. 



It is seen that the time for acquiring these rudiments 



1 See also Mayer, Bull. Mus. Comp. Zool., XXIX, no. 5, 1896. 



