72 COLORATION IN POLISTES. 



INDIVIDUAL VARIATION UNDER VARYING EXTERNAL CONDITIONS. 



In several specimens of P. variatus that were kept in a glass tube for 

 the purpose of learning the time and manner of pigmentation, the 

 pupal period was prolonged much beyond the usual length. This was 

 probably owing to the cold, the average temperature being 1 8 to 24 C. , 

 and therefore far below that under which Polistes usually develops. 

 The imagines in this case were smaller and decidedly more melanic 

 than any obtained from the same nest or even the same region. The 

 yellow was restricted to the merest indication of borders on the ab- 

 dominal segments and two very narrow lines on the metathorax. The 

 rest of the surface was intensely black. One specimen from a nest of 

 gcncrosus obtained from Florida, and under similar observation also 

 came out much more melanic than its congeners. The temperature 

 was in both these cases greatly reduced, for not only was the weather 

 extremely cold for the season (September), but the manner of the 

 keeping of the pupa favored radiation greatly over that usual to the 

 pupa in the nest. The results of a number of experiments in which 

 the external conditions were varied point in the same direction. Our 

 experiments were crude and not at all extensive, owing to the diffi- 

 culty of obtaining material at the time they were carried out. Because 

 of this inadequacy too much stress will not be laid on those results, 

 but the results, as far as any were obtained, are in accord with the 

 hypothesis. A brief account will herewith be given. Two nests from 

 which a number of imagines had previously been obtained under nor- 

 mal circumstances were broken each into four pieces and subjected to 

 the following conditions: (a) Warm and saturated (35 to 42 C.); 

 (b) warm and dry (35 to 40 C.); (c) cool and saturated (about 1 8 C.); 

 (cT) cool and dry (about 18 C.). 



The state of saturation was produced by placing a dish with water 

 in a closed case containing the fragment of nest, the dry ness by the 

 use of CaO. 



From this material not more than four imagines were in any case 

 obtained, with five or six pupae just ready to emerge. Where the 

 conditions were warm and saturated the lateral spot was large and of 

 a reddish orange color, shading at the center into reddish yellow ; 

 where the conditions were cold and dry, although the specimens were 

 from the same nest, the three wasps that emerged after the experiment 

 had been in progress eight days were very black, with narrow, well- 

 defined borders. One specimen had a small yellow lateral dot in the 

 red segment, another a small brown dot, while in the third the second 

 segment was unmarked. Where the conditions were warm and dry, 

 four specimens just ready to emerge showed broad yellow borders and 



