OF ARTS AND SCIENCES. 57 



Indeed, the extremely generalized form of the larvae of this genus is 

 clearly shown by the fact that in P. cecropia, and all the other more 

 specialized and hence later genera, there are only five tubercles on 

 the 8th abdominal segment, those corresponding to the two middle 

 ones of Saturnia having, probably during embryonic growth, coalesced. 

 The embryos of these moths should therefore be examined shortly be- 

 fore hatching to ascertain whether this be not the fact. Meanwhile it 

 is not unreasonable to suppose that all the more specialized genera 

 must have been derived from a Saturnia-like ancestral form, i. e. a 

 larva of cylindrical shape, with all the tubercles, whether thoracic or 

 abdominal, of the same size, shape, and color on all the segments ; 

 those on the 8th abdominal segment being of the same number (six I 

 as on the segments in front. 



The single median tubercle on the 8th abdominal segment of the 

 more specialized Saturnian larvae represents the " caudal horn " of 

 Sphinges, Bombyx mori, and the Notodontian genus Pheosia, and is 

 evidently the result of fusion before the end of embryonic life of what 

 were originally two separate tubercles, like the two separate ones of 

 Saturnia. We are thus able to confirm the suggestion of \V. Muller, 

 who first identified the "caudal horn" with the two dorsal tubercles 

 on the 8th abdominal segment of the Saturniidae.* 



Thus as regards the tubercles the species of Saturnia are on the 



* W. Muller, Siidamerikanische Nymphalidenraupen, 1886, pp. 249, 250. 

 Muller remarks : — 



" So erscheint es berechtigt, f iir das Schwanzliorn der Sphingida die gleiche 

 Genese anzunehmen wie fur den unpaaren Dorn der Saturniada auf 11. Beide 

 sind entstanden aus den Stiitzgebilden der beiden Borsten 1 auf Segment 

 11. . . . Weiter finden sich bei einer Raupe, augensclieinlich den Saturni- 

 den angehorig, in einem friiheren Stadium Sda auf 2, 3, Ds 11 ; mit der nib-li- 

 sten Hautung versebwinden die sammtliehen Dornen. Bei Brohmea led* 

 finden sich im 3. (?) Stadium Ds 11, Sds 2-10, 12, Sst 4-11, von welchen Dor- 

 nen die Ds 11, Sds 2, 3 stark entwickelt, die anderen klein, unscbeinbar Bind 

 Im 1. ( ? ) Stadium sind die Ds 11, Sds 2, 3 wold entwickelt, die anderen Dornen 

 sind kaum nachweisbar. Im letztcn Stadium bleibt nur eine Warze an Stelle 

 des Ds 11 ; es erlialt sich also der Rest von Ds 11, am langsten. 



" Mir scheinen alle diese Griinde zur Annahme zu drangen, dass das Schwang- 

 born der Spbingiden der Rest einer reiclier entwickelten Bedornung ist, einer 

 Bedornung, die vielleicht mit der heutigen der Saturniden auf gleichen I r 

 sprung zuriickzufuhren ist, so dass das Schwanzliorn der Sphingiden mid der 

 Dsdorn dor Saturniden im vollen Sinn homolog sind." 



See also E. B. Poulton in Trans. Ent. Soc. London. 1886, p. 302, and in later 

 papers; also A. S. Packard, Proc. Bost. Soc. Nat. His! , XXV., 1890, pp 99 I" 

 foot-notes 1, 2, 3. Also compare our Figures 3-6, 8 L0 d', and the n 

 to them in the text. Also Grote's N. A. Lepidoptera, Bremen, l-^'>. pp. !'• 



