48 BRITISH LEPIDOPTERA. 



apex of the caudal horn. This would point strongly to the conclusion 

 that the horn represents the base of the unconsolidated pair of 

 tubercles i, the tubercles themselves having disappeared. This 

 disagrees with Poulton's view,* for he looks upon the caudal horn as 

 representing the consolidated pair of tubercles i of the Saturniids. 



The caudal horn of the remarkable genus of Plume moths, Agdistis, 

 does not, according to Bacot, rise from the 8th abdominal segment, 

 and bear the anterior trapezoidals of that segment, as in the Sphingids, 

 but is situated on what is either a small 9th abdominal segment, or a 

 large and distinct subsegment of the 8th abdominal, both the anterior 

 and posterior trapezoidals of the 8th segment being in front of the 

 horn, and in their correct position relative to the spiracle. 



The production of a central row of dorsal tubercles apparently un- 

 paired, in certain families, is very remarkable. This is well seen in 

 the medio-dorsal row of spines in the adult larvae of certain Vanessids, 

 where, too, the real nature of the spines forming this row may be readily 

 learned, by comparing the adult larvae with those in their earlier stages. 

 They are formed by the union of tubercle i on each side, consolidating 

 on the central line of the dorsum. A similar arrangement also occurs 

 in the Saturniids. 



The modifications which tubercles and setaB undergo have been 

 tabulated by Packard, f His table reads as follows : — 



A. — Tubercles. 



a. — Simple and minute, due to a slight thickening of the hypodermis, 

 and a decided thickening of the overlying cuticle ; the hypodermis 

 contains a large unicellular gland, either for the secretion of the seta 

 or for the production of poison. 



1. — Minute piliferous warts (most Tineid, Tortficid and Noctuid larvte). 



2. — Enlarged smooth tubercles, bearing a single seta (many Geometrid and 



Bombycine larvse). 

 3. — Enlarged spherical tubercles, bearing a number of setse, either radiated 



or subverticillate (Arctians, Lithosians). 

 4. - High, movable, smooth tubercles, having a terrifying function (Schizura, 



Xylinodes, Notodonta, Nerice). 

 5. — Low and broad, rudimentary, replacing the " caudal horn " (Choero- 

 campa, Leiocampa (Pheosia) dictaea, and L. dictaeoides). 



b. — More or less spinulose or spiny (disappearing in some Sphinges 

 after Stage 1). 



1. — Long and slender, usually situated on the top of the eighth abdominal 



segment, with microscopic spinules in Stage 1. (Most Sphingidae and 



Sesia\). 

 2. — Smooth subspherical warts (Ghalcosia, East Indies) ; or elongated, but 



still smooth (Attacus atlas). 

 3. — Subspherical or clavate spiny tubercles of many Attaci ; the spinules 



usually short. 

 4. - Spinulated spines or elongated tubercles of Ceratocampidae and Hemi- 



lucidae (Automeris io and Hemileuca viaia, etc.). 

 5. — Spike-like hairs or spines [Saviia cynthia, Anisota, Hypsa (E. Indies), 



Anagnia). 

 6. —Antler-like spines. Early stages of Heterocampa biundata, H. guttivitta 



and H. obliqua). 



* Trans. Ent. Soc. Lond., 1888, pp. 568-574. f Bombycine Moths of America, p. 21. 

 } Packard does not use Sesia in the sense usually understood in Britain, i.e., for the 

 true Clearwing moths, but as a synonym of Macroglossa, 



