246 HABITS AND INSTINCTS IN LEPTINOTARSA. 



alimentary canal, which, on the average, makes 3 per cent, and by the removal 

 of the watery material from the excretory organs and the evaporation from 

 the body surface, which make the remaining 27 per cent. The average dry 

 weight of the beetles does not decrease at all, however, but is rather increased 

 by the excessive feeding that has gone before ; hence in its net dry weight the 

 beetle is heavier when it goes into hibernation than it was when it emerged 

 from the pupa, although its gross weight is somewhat less. 



It is evident that preparation for hibernation consists largely in a reduction 

 of the watery contents of the body and in an elimination of all food and 

 other substances from the alimentary canal. In other words, preparation for 

 hibernation consists in a physiological change in the constitution of the body 

 for the time being and a consequent lowering of the freezing-point of its tis- 

 sues in exactly the same way that the spores of many plants and the over- 

 wintering eggs of Rotifers prepare for the coming on of unfavorable conditions 

 in their environment. Through the loss of water the protoplasm becomes 

 denser, and takes on characters that are at once recognized in cytological 

 preparations. The cells of the body also become shrunken and flattened, 

 the nuclei take on a most extreme vegetative appearance, and in some 

 cases it has not been possible to demonstrate the existence of chromatin in 

 cells where six or eight months later abundant and active chromatic condi- 

 tions will be found. In all of the cells the protoplasm takes on a peculiar col- 

 loidal or else a fine granular appearance and retains it throughout the whole 

 period of hibernation. In the hypodermal cell the lipochrome colors fade and 

 the beetles become light straw yellow, or often white. 



All parts of the body participate in the preparation for hibernation, in which 

 the essential process is the elimination of water until the maximum and min- 

 imum at which the protoplasm of the animal can still survive is increased in 

 both directions to such an extent that lowered or increased temperature will 

 not be likely to produce fatal results. After the beetles have made prepara- 

 tions for hibernation they do not long delay the final burrowing into the 

 ground and the beginning of the long period of dormancy. L. decemlineata 

 hibernates at an average depth of from 18 inches to 2 feet, and I believe that 

 if the winter is very cold it may in some cases work down even farther. 



In decemlineata I have not by any process been able to prevent this prepara- 

 tion for hibernation in beetles which should normally hibernate. By high 

 temperatures and moisture it is possible to greatly inhibit the process, often 

 to the extent that it is not completed, and as a result many of the beetles 

 die. Even if they do not burrow into the ground, the hibernation prepa- 

 ration is completed at the proper time in the life cycle of the species, and, 

 although the beetles are active and out of the ground, they do not feed for 

 weeks at a time, but rest upon the sides of the observation cages or on the 

 food plants. In this way they may pass three or four months, when they 

 again begin to feed, and in a few days are ready for reproduction. 



