46 BRITISH LEPIDOPTERA. 



We find, in definite positions on the larval cuticle, small buttons 

 of chitinous material called tubercles. These usually bear a structure, 

 formerly termed a " hair," but to which the term " seta " is now 

 usually applied, since the seta is not morphologically equivalent or 

 homologous with the hairs of mammals. These setae arise through 

 a modification and hypertrophy of the nuclei of certain cells of the 

 cuticle. According to Dyar, the " primitive form of tubercle consists 

 of a little chitinous button on the skin, bearing a single long hair. It 

 is found in the less specialised groups of Lepidoptera, and exclusively 

 in the Jugate and the Psychids. When this form is present, there 

 are, in general, no other hairs on the body." 



It would appear that in the phytophagous Hymenoptera (Tenthred- 

 inidae), there are well-developed setiferous tubercles, apparently more 

 generalised than those found in any Lepidoptera, but in the Lepidop- 

 tera there appear to be, according to Dyar, two types of arrangement. 

 (1) By far the more generalised, consists, on the abdominal segments, 

 of five tubercles above the spiracle on each side, three in a transverse 

 row about the middle of the segment and two behind, whilst below the 

 spiracle are two oblique rows, containing respectively two and four 

 tubercles. This type is found in Hepialus. (2) The second type con- 

 sists of two dissimilar lines of modification of the first type, of which 

 the fundamental arrangement consists of three tubercles on each side 

 above the spiracle ; three more on each side, below or behind the 

 spiracle and above the base of the leg ; and three (or four) on the 

 base of the leg on the outside, and one on the inside near the mid- 

 ventral line. 



As Dyar has made himself quite an authority on these setiferous 

 tubercles, it may be well to glance at his nomenclature. Commencing 

 from the dorsum, he calls the tubercles above the spiracles i, ii, iii,° 

 the three below, iv, v, and vif ; the group on the outside of the leg is 

 known as vii, and the single one on the inside of the leg as viii. 

 Tubercles vii and viii, Dyar says, are present also on the legless 

 abdominal segments (1, 2, 7, 8 and 9), in a position corresponding to 

 those on the segments bearing prolegs. On the last two abdominal 

 segments (9 and 10) the number of tubercles is always less than the 

 fundamental number, even in generalised larvse. This is evidently 

 due to the fact that these segments have been partly aborted, being 

 without spiracles. The reduction of the ninth abdominal segment 

 has taken place on the anterior portion, whilst the tenth abdominal 

 has lost the lateral part (Classification of Lep. Larvae, pp. 196-7). Dyar's 

 conclusions as to the relationship which the lepidopterous super- 

 families bear to each other are based on (1) The position of the 

 tubercles with regard to the sub-segments into which the abdominal 

 segments are divided. (2) The tendency for tubercles iv and v (the 

 post-spiracular and sub-spiracular tubercles) to coalesce or separate. 



As to their position, Dyar says that in the Jugate (Hepialids) the 

 three tubercles of the middle sub-segment are all present, and the 

 upper and lower of the posterior sub-segment. In the Psychids, the 

 three tubercles are retained on the middle sub-segment, but both are 



* i = anterior trapezoidal, ii = posterior trapezoidal, iii = supra-spiracular. 



f This is a secondary tubercle, absent usually in the newly hatched (gene- 

 ralised) larva of the higher families. Hence its importance is less valuable than 

 Dyar afterwards insists, when discussing the Psychids and Micro-fkenat/e. 



