i64 ENxpMOLOGiCAL NEWS [June, '20 



blood food. This fact is of some interest when compared 

 with the behavior of Chionea. While Chionea as a winter 

 insect is normally negatively thermotropic, in the mosquitoes 

 the thermotropic reaction appears to be absent in the winter 

 months, when the insects cannot fly about and therefore 

 cannot obtain blood food. More observations, however, are 

 necessary to gain a complete insight into these phenomena. 



Concerning other bloodsucking insects, so far no data are 

 available. Hog lice, Haematopinus siiis, failed to give a 

 thermotropic reaction but this appears not astonishing since 

 these insects live permanently on their host, and being wingless, 

 would hardly be able to find the host by means of a tropism. 



A distinction should be made between a mere aggregation 

 of insects in a definite temperature-optimum and a true 

 thermotropism in which there is an oriented movement in 

 the direction of the source of heat, or away from it. Olive 

 C. Lodge (1918), found that house flies will congregate around 

 a Bunsen burner in a definite circle, the size of which varied 

 according to the distribution of the heat. This was tested 

 by placing larger or smaller pieces of asbestos over the flame, 

 when the flies arranged themselves in larger or smaller circles 

 respectively. The temperature of these circles was very 

 constant, varying between 42 and 44°C. If the gas was 

 turned off the flies came nearer the burner and climbed up 

 the stem of it, but when it was no longer warm they dispersed 

 in all directions. Heated baits were visited most frequently 

 when their temperature was at 38-48°C. The impression 

 is gained that the flies prefer a definite optimum of tempera- 

 ture, but it remains to be seen whether there is any specific 

 reaction to heat, as is apparently the case in the mosquitoes. 



The problem, what particular sense-organs of the thermo- 

 tropic insects are affected by the radiation of heat from ob- 

 jects producing the reaction, seems not yet entirely solved. 

 According to Graber (1882), whose experiments were men- 

 tioned, the sense of heat (Warmesinn) is developed, at least 

 in Blatta, chiefly in the antennae, and to a lesser degree in the 

 cerci (Analborsten). The functional interpretation of the 

 well-known specific nerve endings of the antennae has there- 



