20 BRITISH BUTTERFLIES. 



as tubercles ii, or the posterior trapezoidals. Another row is found 

 along the side just above each spiracle, these are known as tubercles 

 iii, or supraspiracular tubercles, another row is placed just behind each 

 spiracle, called tubercles iv, or postspiracular (in many superfamilies 

 of the lepidoptera tubercle iv is subspiracular like v), whilst a row placed 

 directly under the spiracles are called tubercles v, or subspiracular. 

 At the tops of the outside of the prolegs is another series known as 

 tubercles vii, or marginal tubercles, whilst between v and vii is a row 

 of secondary, rather than primary, tubercles, known as tubercles vi. 

 These should be thoroughly worked out by every lepidopterist who 

 wishes to study the structure of butterfly larva?, and particularly to 

 describe them. We have already stated that the position of those on 

 the thoracic segments is often much modified, and their homologies 

 are not always easily to be determined. The differences in character 

 and position between the corresponding tubercles on the different 

 segments are of the greatest possible importance, particularly is this so 

 in the case of a comparison between the positions of those on the 

 thoracic and abdominal segments. 



Besides the hairs or seta? carried by the tubercles, which have fairly 

 fixed positions in all butterfly larva?, the skin of most butterfly larvae 

 has, scattered more or less regularly over the body, little elevations, 

 resembling somewhat a fine pile or covering of minute hairs. This 

 pile is a very common feature in butterfly larva?, is supported by very 

 minute papilla?, and is generally distributed with considerable regularity, 

 usually in a transverse, though sometimes in a longitudinal, direction. 

 It is, however, occasionally scattered irregularly over the body, and 

 when it is arranged transversely, it- is usually somewhat closely related 

 to the subsegmental divisions into which the segments are subdivided. 

 It is not at all confined to butterfly larva?, but is found very generally in 

 those of many other superfamilies. As an illustration of the vagaries 

 connected with its appearance one may note that in the larva of Aylais 

 urticae it is strong in the early stages, whilst in that oiZephyrus quercus 

 it is strong when, and not until, the larva is fullfed. Scudder thinks 

 that "the clothing prevents the too rapid evaporation of the heat from 

 the surface of the body, for, although larva? are cold-blooded animals, 

 they, nevertheless, have an internal heat above that of the surrounding 

 atmosphere, which originates from the activities of the organs and the 

 respiratory functions, and which they would lose more rapidly but for 

 this investing pile." 



Many larva? are provided with what may fairly be termed glandular 

 hairs. They are more especially abundant in young butterfly larva 1 and 

 occur in all the larval stages among the Saty rids and Pierids. InthePieritls, 

 they form an open basin, fringed with cilia, supported on an exceedingly 

 slender hollow pedicel. In the basin a drop of transparent fluid may 

 be secreted when the hairs look as if tipped with dew. The purpose 

 of the secretion is possibly protective, as the volume of the 1 fluid is visibly 

 increased when the larvae are excited. Scudder writes : "They are generally 

 arranged in longitudinal rows, and their use is wholly unknown, but 

 they probably have a, protective function, lor i his Quid is odoriferous, the 

 secretion increasing when the larvae are disturbed." He describes them 

 as " papilla-mounted bristles, each furnished with a, trumpet-mouthed 

 tip," and adds thai they "are the duets Leading from glands at theii 

 bases, secreting a transparent fluid, which, after secretion, is borne in a, 



