1899.] NATURAL SCIENCES OF PHILADELPHIA. 137 



igm of such a coat of pigment would be to place it in closer tlienuic 

 relations to its surrounding. By virtue of it the organism could 

 absorb a greater amount of radiant energy from an external source 

 of greater intensity, but it would also lose its internal heat more 

 rapidly to a cooler medium with which it was in contact. This 

 being the case, it seems impossible to apply Lord WaLsingham's 

 ('85) hypothesis, valuable though it may be when applied to insects 

 alone, to our worm. Lord Walsingham calls attention to the very 

 striking fact that while many warm-blooded animals become white 

 when subjected to Arctic conditions, the very opposite takes place 

 in insects. He points out that it is vitally necessary for a homo- 

 thermic animal to retain as much as possible of its internal heat 

 ■during cold weather. A white coat favors this. An insect, on 

 the contrary, having a variable temperature, becomes dormant 

 Avhenever the external temperature falls below the minimum for its 

 metabolic activity, but becomes more and more active with increas- 

 ing temperature. In Arctic chmates the season of acti%'ity for 

 insects is very short. It is manifestly advantageous, therefore, 

 that during it, metaboUsm be as rapid as possible. Increased capac- 

 ity to absorb radiant energy would therefore be beneficial. 



Inasmuch as the snow- worm does not, according to Mr. Bryant's 

 account, expose itself to the sun's rays, it cannot benefit by its 

 capacity to absorb heat rays, except possibly during the short 

 period when it lives in the glacier pools. Even if they were to 

 come to the surface of the snow while the sun shone, it seems to me 

 that they could gain no appreciable amount of heat. The heat 

 absorbed would be immediately transferred to the surrounding snow, 

 which would melt, and the worm would simply tend to sink beneath 

 the surface. This would be the only change resulting from its 

 capacity to absorb heat rays. Zoological literature fairly bristles 

 with attempted explanations of melanism. Some are simplv 

 attempts to correlate melanism w'ith certain factors of the physical 

 environment; others are more or less ambitious essays to explain 

 the general fact or special cases. "Without seeking to exhaust 

 the field, I have applied more than a dozen of them to thn case of 

 this worm, without finding one that fits all of the conditions. 



The Oligochseta are generally associated with warm, moist situa- 

 tions. We meet with them mostly during the spring and early sum- 

 mer months, while during the winter they retire from sight by 



