34 BRITISH LEPIDOPTERA. 



Scudder draws special attention to the confusion which has arisen 

 among entomologists as to the application of the terms " maxillae " 

 and " maxillary palpi." He says that " ideally, and sometimes 

 actually, the maxillae of insects bear three palpi, any one of which may 

 become specially developed and receive the name of maxilla, while the 

 others are termed palpi, thus the organ called maxilla in one group is 

 not always strictly homologous with that which bears that name in 

 another group." 



The segments of which the thorax and abdomen are composed are 

 very much like one another, especially in the earlier stages, but they 

 sometimes become considerably modified in size, shape and appearance, 

 as the caterpillar gets older. The segments, both of the thorax and 

 abdomen, are usually more or less distinctly subdivided transversely 

 into sub-segments or annulets. The first thoracic segment is some- 

 times considerably modified, constricted in Hesperid larvas so as tp form 

 a neck, swollen in the larvae of Lycaenids, Papilionids, and" many 

 moths, so that the head is quite retractile. In Papilionid larvae, also, it 

 bears on its dorsum a forked scent-gland or osmaterium, hidden in a 

 narrow transverse slit when not in use ; in the larvae of butterflies, 

 Notodonts and Noctuids, it frequently bears on its lower surface a 

 remarkable structure, known as the " chin-gland." This is an eversible 

 gland, and one modification of it is found in the syringe of the 

 Dicranurid larvae. This, the larva of Centra vinula uses as an offensive 

 weapon, ejecting formic acid from it with considerable force. .Of the 

 abdominal segments, the last, the anal segment, is the most modified. 



The spiracles or stigmata, as we have already seen, are placed in 

 pairs, one spiracle on each side of the first thoracic and first eight 

 abdominal segments. Chapman was the first to discover that they 

 were, occasionally, found in lepidopterous larvae on the second and third 

 thoracic segments. Packard afterwards discovered the clustered 

 tracheal tubes, belonging to these segments, in a Sphingid larva, and 

 in that of Plutymmia cecrojna, but without any external sign of the 

 spiracles. Scudder found spiracles on the second and third thoracic 

 segments in the young larva of Pawiihila mandati. The cause of the 

 usual absence of spiracles on the meso- and meta-thorax, is probably 

 due to the fact that, on these segments, the future wings are, during 

 the larval existence, in process of development. Chapman observes 

 (Ent. Rec., ix., p. 219) that, although there is no larval spiracle on the 

 meta-thorax in Charades jasiws, yet, when the larva undergoes its final 

 ecdysis, and becomes a pupa, a tracheal lining is drawn out between 

 the 2nd and 3rd thoracic segments, where the imago has, but the larva 

 has not, a spiracle. Chapman states that, although the casting of a 

 tracheal lining from the 2nd thoracic spiracle had not been observed 

 by him before he saw it in this species, he had inferred that such 

 occurred, because he had seen it many years ago in numerous larval 

 moultings (first, in the large silkworm, Antlieraca i/ama-iiKii). and had 

 also demonstrated the existence of this spiracle in the imagines. 



The spiracles are placed laterally, usually, a little below the middle 

 of the sides, in the centre, or a little in front of the centre, of the seg- 

 ments of the abdomen. The pro-thoracic spiracle is placed near the 

 hind margin of the pro-thorax. They are sometimes very distinct, at 

 other times inconspicuous, usually with thickened lips, frequently of 

 an oval shape and with a raised outer margin. The spiracles on the 



