1914] Longevity of Insects 341 
awaken the snail, as the carbon dioxide and dehydration 
plunges it into sleep. The amount is the essential to sleep or to 
awakening. Janichen (25) believes that the theory of autonar- 
cosis of carbon dioxide should be held for all cold blooded 
animals. 
The histological changes of hibernation have been studied 
in the hedgehog by Carlier (9). Plasma cells with deeply 
staining granules and with lightly staining nuclei are present 
in great numbers in the base of the tongue—they have the 
appearance of overfed cells although the fact that they are not 
found far into the digestive tract, seems, he states, to contradict 
this appearance. During hibernation the granulations dis- 
appear and the tissues of the tongue are less stainable. Num- 
bers of the wandering white blood corpuscles are destroyed by 
macrophags and their number is recuperated all during hiber- 
nation by karyokenetic division in the lymph glands. During 
this period, some liver cells increase in size followed by an en- 
largement of the nucleus until the latter, having overstretched 
the nuclear network, ruptures and disappears—this Carlier 
believes to be the natural death of the cell. 
Insects usually hibernate towards the end of summer when 
the temperature is falling but they are also known to go into this 
condition even though placed at a high temperature. Tower 
(53) found in his experiments with the potato beetle that he 
was unable under any laboratory conditions of high temperature 
to bring the beetles into hibernation at an unusual time. Sand- 
erson (47) found that tent caterpillar eggs will not hatch if 
placed in a green house before being exposed to low temperature, 
while those which stay out of doors until the temperature falls 
will hatch rapidly at green house temperature. Merrifield 
(34) concluded from his experiments with seasonal dimorphism 
that there is probably a strong tendency for individuals to take 
either the winter or the summer form in spite of all temperature 
treatments. 
Weismann found that summer forms could be obtained in 
winter (55), by chilling a pupa and then subjecting it to heat, 
while on the other hand, if the pupz were put immediately at a 
high temperature, they did not hatch until summer. There is. 
further data to show that low temperature is in many cases not 
the only factor in hibernation. Foster (*) states that of seven- 

* Life History of the Codling Moth, U. S. D. A. Bur. Ent. Bul. 97, Part 2, 
Foster. 
