404 THE AMERICAN NATURALIST. [Vol. XXXVI. 



eleven minutes. In this case the critical point is — 9.4° C, and 

 — 1.4° C. is the normal congealing point. This insect revived within 

 an hour after the experiment, and laid eggs on the following day. 

 From this Bachmetjevv concludes that the mere congealing of the 

 body fluids is not lethal. In a second experiment a moth of the same 

 species showed a critical point of — 11.6° C. (4.25 p.m.), whereupon 

 the temperature rose at once to — 1.1° C. The insect was kept in 

 the cold, the temperature of its body again sinking to — 15.6°. At 

 6.15 P.M. it was removed to the temperature of the room, but could 

 not be revived. It follows that the insect dies if its body is still 

 further cooled after the rebound (the limits being not necessarily 

 higher than — 2.5° C. nor lower than — 15.6° C), or, as a general rule, 

 it may be stated that the insect dies if its temperature be again 

 reduced to about the point from which it rebounded. Further exper- 

 imentation on this interesting subject led to the following general 

 conclusions here briefly transcribed. The extreme degrees of under- 

 cooling of the fluids differ in different insects, and these extremes 

 occur at nearly the same rate of cooling. The critical point, so far 

 as its absolute minimum is concerned, is greater in pupte than in 

 imaginal moths and butterflies, whereas the maximum differs in pupae 

 and imagines. Owing to lack of material, the behavior of the larvae 

 could not be determined. With respect to sex, the degree of under- 

 cooling of the fluids in normal specimens is lower in the males than 

 in the females. This is also the case after brief fasting ; after pro- 

 tracted fasting, however, the degree of undercooling is lower in the 

 males, but finally becomes the same in both sexes. On the other 

 hand, the normal congealing point of the fluids is lower in the females 

 than in the males. After fasting, it is the same in both sexes ; but 

 after protracted fasting, the relation is again reversed. Further 

 investigation of this question showed that the insect juices have a 

 lower critical point when the insect is fasting, but so far as its abso- 

 lute magnitude is concerned, it diminishes on continued starvation. 

 Repetition of undercooling gave the following results: On freezing 

 a second time strong Lepidoptera exhibit a much greater degree of 

 undercooling than on the first freezing; on being frozen a third time 

 the fluids show almost no undercooling. This is also shown by weak 

 Lepidoptera on the second cooling. Bachmetjew also studied the 

 influence of the fluid coefficient on undercooling. If J/ be taken as 

 the total weight of the living insect, and P its weight after drying on 

 a water bath for a long time at a temperature of 115° C, M — P 



