THE EXTERNAL STRUCTURE OP THE LEPIDOPTEROUS LARVA. 51 



The varied stages of development of the setiferous tubercles, some- 

 times reached in allied genera in the egg, is of the highest significance, 

 as is also their comparative development in the various stages of the 

 larvae of allied genera, as in Omithoptera and Papilio, in Aylia and 

 Citheronia; whilst Packard* states that the "tubercles of the adult 

 larvae of Saturnia (pavonia and pyri) are on the same plane with the 

 embryo, just before exclusion, of the more highly specialised forms of 

 the group Attacinae," and, again, "whilst the late embryos of the 

 Attacinae are, perhaps, paralleled by the fully-grown larva of Saturnia, 

 the fully-grown larva of the most, or one of the most, generalised of 

 the Attacinae, Platysamia, is on the same plane of specialisation as 

 the larva of Callosamia in its third stage." 



The larvae of a large number of Lepidoptera are provided with what 

 may be fairly termed glandular setae. They are more especially 

 abundant in young larvae, and occur in butterflies (Pierids and 

 Satyrids), Geometrids (Ortholitha cervinata), Notodonts (Datana, Dasy- 

 lophia), and many others. Packard describes the glandular hairs of 

 newly-hatched larvae of Ceratosia tricolor as " flattened at the tip, 

 which is slightly tridentate, with grooves passing down the shaft 

 from the notches between the teeth." In the Pierids they form an 

 open basin, fringed with cilia, supported on an exceedingly slender, 

 hollow pedicel, the hairs looking as if tipped with dew. 



In a preceding part of this chapter (p. 40), we query the absence of 

 the paranal forks in the Rhopalocera. This is because Chapman has 

 called attention to a well-known structure, called the " anal comb," 

 which is possibly homologous with the paranal forks. It is found just 

 under the anal flap in many Tortricid, Hesperid, and Pierid larvae. 

 Scudder figures the anal comb in Colias (Ewymus) philodice, but does 

 not seem to mention it in the text. This should, of course, have been 

 mentioned directly after the paragraph referring to the " paranal 

 forks." 



It has been repeatedly noticed that certain larva?, when confined, 

 have a tendency to crawl upwards, and this is more particularly the 

 case with some species than others. Larvae of the genus Coleophora, 

 Aglais tirticae, Vanessa io and others, might be instanced as always 

 taking possession of the highest possible point of any receptacle in 

 which they may be placed. Poulton suggests that this is due to the 

 fact that the larvae in these movements are guided by an appreciation 

 of the force of gravitation. That it is not always in order to seek 

 food is evident, for the larvae will crawl over the food-plant in order 

 to reach the highest available point. It is very possible that these 

 movements are made in order to seek light, or air. At any rate, 

 it is not yet at all clear how far the latter causes are factors in bring- 

 ing about these movements, and how far the force of gravity has 

 effect. 



Poulton further considers that the force of gravity has been 

 potent in bringing about the characteristic " Sphinx-like" attitude that 

 characterises the larvae of certain Sphingids, Aglia, etc. This atti- 

 tude, he says, bears a distinct relationship to the position assumed 

 by these larvae. The thoracic legs, in such larvae as adopt this 

 attitude, are not used for the support of the body, and, hence, when 



* " Studies in the Transformation of Moths of the Family Saturniicte," Proc, 

 Amer. Acad, Arts and Sciences, 1893, 



