G. GENERAL NATURAL HISTORY AND ZOOLOGY 219 



gests that it is connected with exposure to a stormy atmos- 

 phere. He observes, farther, that many of the winged spe- 

 cies have wings more developed than usual; and Mr. Darwin, 

 applying his peculiar views of selection to the case, gives as 

 the explanation that the act of flying exposes the insects to 

 be blown out to sea and destroyed, and those that flew least 

 lived the longest, and by that process the race became ap- 

 terous. On the other hand, with species to which flight was 

 a necessity, the strongest-winged lived the longest, and thus 

 their wings became more and more developed in each suc- 

 cessive generation. 12 A, March, 30, 435. 



SELECTION OF INSECTS FOR FOOD BY BIRDS. 



Although we look, and with ample reason, to the birds as 

 the main agency in destroying insects injurious to vegetation, 

 observation shows that different forms of insects are molest- 

 ed by them in very different degrees. This is especially the 

 case in regard to the Lepidoptera, some forms of which are 

 not touched by any birds whatever, and others, again, are de- 

 voured by some and spared by others. As a general rule, it 

 is said that the most beautiful and brilliantly colored Lepi- 

 doptera owe their safety to their tints, as the bird first at- 

 tacks the most striking portion, namely, the red hinder wing, 

 and the insect tears itself away and escapes. Hairy caterpil- 

 lars, again, are less eaten than the smooth species, not only, 

 perhaps, on account of their bristly covering, but their more 

 nauseous taste. The streaked caterpillars, spotted with yel- 

 low, are usually refused, while all the smooth and dark kinds, 

 especially those resembling plants in color, or of a reddish 

 tint, are generally devoured with great avidity. 1 (7, xxni., 

 368. 



TEMPERATURE OF INSECTS. 



The delicate indications in regard to temperature furnished 

 by the thermo-electric apparatus have been lately used to 

 great advantage in many investigations having for their ob- 

 ject the determination of minute quantities of heat. Some 

 of these we have already presented to our readers, and we 

 have now to chronicle some new experiments with the appa- 

 ratus, for the purpose of ascertaining the amount of heat pos- 

 sessed by invertebrate animals, in continuation of the re- 



