ESTIVATION AND HIBERNATION. 249 



the gross weight due to the loss of water. There is, however, no loss in the 

 dry weight during this preparation for aestivation. Yet even when fully pre- 

 pared for the advent of the dry season, the beetle does not at once enter upon 

 the dormant state, but may live in a rather inactive condition upon its food 

 plant for days or even weeks before it burrows into the ground to pass the 

 dry season. When, however, the dry winds come at the cessation of the 

 rains, the beetles usually seek retirement in the ground, but they do not now 

 burrow down more than 6 or 8 inches, and often may be found within only an 

 inch or so of the surface. They remain in aestivation until the rains come at 

 the beginning of the following season, when they are awakened to renewed 

 activity and another series of generations. On emergence from aestivation 

 they go through the changes found in the preparation therefor, but in reverse 

 order. 



The preparation for aestivation in undecimlineata results in a reduction of 

 the water content of the body, and hence in au increase in its capacity to meet 

 the high temperatures which often occur, especially at the end of the dry 

 season, when the lack of moisture and the intense sunshine in a cloudless sky 

 heat the soil up to a high degree. Soil temperatures taken on the savannas 

 of Vera Cruz in April, 1904, in places where these beetles were aestivating, 

 were frequently as high as 60° and 65° C. It is for the purpose of success- 

 fully passing through these high temperatures at the end of the dry season 

 that the physiological changes involved in aestivation are due. Moreover, in 

 the same regions the temperature frequently falls rather low at night during 

 the dry season, although there are never frosts, 3° C. being the lowest re- 

 corded temperature. 



With multitcEniata, which lives on the cold, dry plateau, the preparation for 

 aestivation is the same as that described for the two preceding species. This 

 form has to encounter in the dry season not only high temperatures by day, 

 but also freezing conditions at night, and great desiccation at all times for 

 seven or eight months of the year. Although the environment differs greatly 

 in the three species, the manner of preparing for the season of the year when 

 unfavorable conditions of existence are most apt to obtain is the same in all. 

 The process is simply that of storing up a reserve food supply in the fat-body 

 and removing all matters which might ferment, decay, or become poisonous 

 to the animal, and the reduction of the water content to a lower percentage. 

 It is this last which gives to the organism the ability to resist the extremes of 

 temperature and moisture which it surely will encounter in the course of the 

 ensuing winter or dry season. The concentration of the protoplasm very 

 greatly widens its range of existence for the time being. This concentration 

 of the protoplasm in hibernation and aestivation has been studied much in 

 plant spores and in the lower animals, and the general conclusion has been 

 reached that increased capacity to resist high or low temperatures or extreme 

 desiccation is always due to the loss of water in the protoplasm; and like- 

 18— T 



