Ii8 



than Arterias, because in the former the warts are still visible in the 

 fourth stage, and the markings are not so fully developed as in the 

 corresponding stage of Asterias (see Edwards). 



The bright-colored saddle, which interrupts the prevailing dark color, 

 is found in these two species, and in a somewhat similar form— as ob- 

 lique bands — in Papilio Troilus and Ticrnus, as well as in other cater- 

 pillars, such as Limenitis Arthemis (see Edwards). Interrupting the 

 dark outline which makes the caterpillar visible at a distance, the saddle 

 may serve to render it less conspicuous, less easily detected by its 

 enemies. 



Papilio Philenor occupies an exceptional position among its con- 

 geners, but is on that account none the less interesting and instructive. 

 The first stage corresponds substantially to that of the other forms, 

 but after that period the development takes another direction. The 

 bristles vanish, it is true, but not the warts; on the contrary, these 

 become longer and grow into horn-like appendages. This process, 

 however, takes place only on the thoracic and the last abdominal rings; 

 in fact the longest horns stand on the first thoracic and the last ab- 

 dominal. 



In this species also the warts are suppressed on the middle segments, 

 but only gradually, and even after the last moult they still remain visi- 

 ble. In the infrastigmal row they still remain very long. 



While the coloring and markings of P. Philenor are of secondary 

 importance, the warts are inherited from the prototype, and have been 

 chosen by natural descent as the objects of its formative power; here, 

 too, the bristles vanish and the long horns are perfecdy smooth. I see 

 little reason to doubt that we must regard these horns as means of in- 

 spiring terror, especially those standing on the thoracic segments. 

 Those on the last abdominal segments, as I have before intimated, 

 probably owe their origin to a correlative transfer of the thoracic for- 

 mations to the abdominal rings. Correlation may also account for the 

 fact that the warts remain so long on the infrastigmal row, as the pur- 

 pose which they subserve for the insect is not easily perceived. The 

 formidable horns on the thoracic segments belong to the infrastigmal 

 series, and it may hence be inferred that on the remaining segments 

 also there would be a tendency to enlarge, or at least to maintain, the 

 corresponding warts. 



Turning our attention to the form of the bristles standing on the 

 warts of the Papilionidcc , we see that in the first stage they have a long 

 shaft and a shovel-formed, enlarged extremity. This typical form I 

 have found in all the Prf/'z7zw2Zrt'^^' which I have examined; and although 

 Ajax is an exception with its bifurcate bristles, yet even this form, as 

 I have already remarked, reverts to the other, as the furcate division 

 may be regarded as a widened extremity. 



