JMEMOIKS OF THE NATIONAL ACADEMY OF SCIENCES. 21 



■"111 otlior o-oiicra of this luiiiily, as tlic .species of Ocinaia. in wiiicli the lindy is slender, tlicre 

 is a caudal horn. In < >. signifera there \s a well-developed caudal horn, while the body is 

 iumiped on the second thoracic, second and fifth aV)doniinal seoiiients. Indi'ed. it ))ears a close 

 resenihlanee in general appeai'ance to certain oeometric or nieasurinti- worms, such as Ennomos, 

 Eutrapela. Eiio'onia, etc. 



"It is worthy of notice, as ))earini;- on the use of these h()rn-lil<e tuhiM'cles as offensive struc- 

 tures, that Captain Hutton states that the extremity of the iiorn is retractile and is generally 

 withdrawn into the lower part a.s a sheath; when the animal is about to molt, or is disturbed 

 and irritated, the summit of this spine is exserted, and instead of Ijcing brown, like the base, is 

 whitish; Avhen exserted the whole stands erect, slightly inclining backward." 



Horstield and Mooi'e figure the larva of 0. d'dectxda of Java as having a horn. 



The caudal horn of the SphingidR'. — Much has been written on this subject. In 1882 Mr. 

 Meldola. in the appendix to his translation of "Weismann's "Studies in the theory of descent," 

 calls attention to the caudal horn of sphinx larva\ mentioning that in the j'oung larvie it is "freely 

 movable," adding: ''It is possible that this horn, which was formerly possessed by the ancestors 

 of the Sphingida?, and which is now retained in many genera, is a remnant of a flagellate organ 

 having a similar function to the head tentacles of the Papilio larva' or to the caudal appendages 

 of Dicranura." 



Poulton (18S4) concludes that the forking of the horns is a primitive character and observes 

 that it is movable in the two first stages of S. Ji(iusfri and under the control of the animal's will. 

 He also cjuotes notes from Mr. K. Trimen on the young larva of Lophoxfetlms dumoIi?iii Angus, in 

 which it is stated that the anal horn is, like the dorsal thoracic spines, "distinctly forked" at the 

 extremity. Mr. Meldola adds that "the forked caudal horn in the young larva of this species is 

 of interest in connection with the similar character of this appendage in the young caterpillar of 

 Uy/oicns pinasirP'' (p. 527). 



The caudal horn of the fully grown larva of Loplionfethvx. diimolhiu, which is well figured 

 by Lieut. Col. J. M. Fawcett," differs from that of all other known sphingid caterpillars in being 

 a solid chitinous spine, sharp, not forked, and with several setaj, being in fact, judging by the 

 figure, no stouter, longer, or differing in any respect from the thoracic horns. 



Willielm ]\Iuller, in 1886, at the close of his memoir, figures the end of the body of the larva 

 of Diloptonota and discusses the caudal horn of the Sphingid a\ considering that it has the same 

 origin as the unpaired horn of the Saturniida\ remarking: " Both have arisen from the supporting 

 structures [tubercles] of the two bristles upon segment 11." He concludes that the caudal horn of 

 the SphingidcV is the remains of another armature perhaps referable with that of the Saturniida? of 

 the present day to a common source, so that the caudal horn of the Sphingida^ and the caudal 

 spine {Ds horn) of the Saturniida^ are in the fullest sense homologues. 



The present writer has paid especial attention to the double nature of this tubercle in the dif- 

 ferent groups and genei'a of the Ceratocampida\ Heniileucid;e. and Satui'iiiida", the facts being- 

 stated in the course of the description of the larvw in different stages and affording strong proofs 

 of its origin from the fusion of the two tubercles /. 



Besides the caudal horn of Ceratomia, already described. I have previously stated* that in 

 stage I of Paonias exciecatas the caudal horn is distinctly forked at the tip, and that in stage III 

 it ends in two tubercles. In Sphinx Ixdmix in its second or thii'd stage the iiorn ends in three 

 or four tubercles, but in stage IV? there are no definite traces of a fork. In a Sphinx found on the 

 larch the horn is smooth, but ends in two fine setie. In a lot of freshly hatched Sphinx larva of 

 an unknown species the horn is distinctly forked. 



In a full-grown Sj)hi)i.r chi-rsis the end of the horn is smooth and undivided. PI. XLII, 

 Fig. 3, represents the end of the caudal horn of I'aonias myops. the tip ending in two rounded 

 smooth tubercles without a seta, though the rounded spinules below each bear a distinct seta; 

 a represents the tip as seen from the end, showing the rounded ends of the fork. 



"Trans. Zool. Soc, London, XV, April, 1901. 



^Proc. Boston Soc. Xat. Hist. XXV, p. 103, footnote, 1890. Compare also C. M. Piepers, Ueber das Horn der 

 Sphingiden-Raupen, Tijdschr. v. Ent.. XL. 



