PSYCHE. 



lavs), and also about the seventh abdom- 

 inal segment, by the tendency of both 

 markings and dermal appendages to 

 assume a polar arrangement in elong- 

 ated forms. By this means arose 

 through the intensification of these 

 contrasts the lightening of the middle 

 parts of the body to form a saddle- 

 shaped, whitish patch — a marking 

 surely of great antiquity in swallow- 

 tail caterpillars, since it is now found 

 at birth in four of our six genera, and a 

 fifth shows a tendency toward it. This 

 style of marking has been retained 

 throughout life in Heraclides only of 

 all the members of our fauna ; and as it 

 it is in just this genus alone that the 

 lenticle-traces ot the tubercles persist to 

 maturity, we have certainly in Hera- 

 clides the perpetuation of a very anti- 

 quated type. 



That in Papilio we have also a very 

 persistent type may be judged from the 

 great stability of the upper tubercles, 

 which are even not lost until after the 

 assumption of the changed livery of 

 maturity, — a livery which owes a part 

 of its variety and enlivenment to ex- 

 change of some of these tubercles for 

 bright colored spots ; these break up 

 the transverse black stripes in a vari- 

 able degree, and the stripes themselves 

 appear to be but little more than reten- 

 tion of parts of the original color (fixed 

 at the particular spots they occupy by 

 the central position of the black tuber- 

 cles) when the green livery of adult 

 life is assumed. For it seems to be a 

 green resembling the green of the 

 leaves upon which the caterpillar lives, 

 that is the ultimate aim of most Papili- 



onid coloration. In caterpillars of their 

 size other colors would be too conspic- 

 uous for their advantage, and varia- 

 tion in this direction would be natural. 

 Moreover, it is the color reached or 

 partly reached, in several different ways, 

 as the development of the other types 

 show ; thus in the other striped cater- 

 pillar, Iphiclides, the stripes grow 

 obsolescent toward maturity and leave 

 the caterjaillar more completely green. 



We may then trace several lines, to 

 a certain extent parallel, along which 

 the modification of the caterpillars of 

 Papilionini has developed, parallel at 

 least in that the loss of the juvenile 

 bristles has been universal but at differ- 

 ent stages; also that the loss of the 

 juvenile tubercles has been universal 

 though not always complete, their loss 

 being generally made good by lenticles 

 and these by spots ; and sometimes, by 

 acceleration, a phyletic stage is set 

 further and further back and finally, 

 perhaps, crowded out. 



One of these lines, very distinct from 

 the others, is found in Laertias, which 

 has developed to so high a degree that 

 its juvenile bristles, themselves excep- 

 tionally simple, are completely lost 

 with the earliest stage ; so, too, most 

 of the tubercles ; but here a very curious 

 change occurs : those which are lost 

 are replaced in new positions by others 

 entirely different, which take on a more 

 elongated form and become more prop- 

 erly fleshy filaments ; while those which 

 remain assume also the new develop- 

 ment. The dark and almost uniform 

 color of the larva throughout life is to 

 be explained probably by acceleration ; 



