Vol. XXXl] ENTOMOLOGICAL NEWS l6l 



Among insects, cockroaches are known to prefer warm 

 places, and so undoubtedly do numerous other insects. In 

 fact, an attraction by heat must be quite general, and is 

 probably found at the bottom of such instincts as that of 

 ants to bring their offspring to the surface of the earth when 

 the stone covering the colony is heated by the sun's rays. 

 Subterranean larvae also probably move upward and down- 

 ward with regard to temperature. While roaches and domes- 

 tic crickets seek the heat of the stove, the field crickets, 

 ground beetles, etc., are found in places exposed to the full 

 sunlight. Hairy caterpillars, like those of Malacosoma, 

 seek the sunshine and apparently derive advantages from 

 being heated by the sun's rays, but whether they are attracted 

 by a purely thermal stimulus is doubtful (Howlett, 1910). 



Graber (1882), to whom we owe so many fundamental 

 observations concerning the function of sense-organs in lower 

 animals, seems also to be the first to have noticed tempera- 

 ture reactions of insects. According to this author, who 

 experimented with the cockroach Blatta germanica, the an- 

 tennae of Blatta are more sensitive to certain extremes of 

 temperature than are, for instance, the lips and finger-tips 

 of man, which are the most sensitive parts of the human body 

 as regards temperature. 



If a specimen of the Blatta is blinded previously to the 

 experiment, and then its antenna approached with a red-hot 

 needle or with the point of a very cold object, the stimuli 

 thus afforded will produce an effect even at a distance from 

 which the human skin does not perceive any sensation, the 

 effect on the animal being that the affected antenna is with- 

 drawn. 



Graber's observations show that there is in certain insects 

 a highly developed sense of temperature, but the behavior 

 of Blatta in his experiments cannot be called a tropism in 

 the ordinary sense, which would involve oriented movements 

 in which the orientation of the animal is affected by its 

 reactions. 



Observ^ations on what appeared to be a negative thermo- 

 tropism, were made by the writer (Marchand, 19 17) on the 



