ESTIVATION AND HIBERNATION. 247 



Upon emergence from hibernation changes are found which are the reverse 

 of those which take place in the preparation for hibernation. Immediately 

 upon emergence a beetle voids the waste products that have accumulated in 

 the malpighian tubules, and, if food is at hand, begins to devour it most rav- 

 enously, so that it increases in weight with marvelous rapidity, until in three 

 or four days from the time of emergence it weighs more than it did at the 

 beginning of the preparation for hibernation. The beetles on emergence from 

 hibernation weigh less in both net dry and gross weight than they did at the 

 beginning of hibernation, which shows that there has been a low grade of 

 metabolism going on throughout the period of hibernation. 



We see that there is a rapid gain in the water content of the body as well as 

 a net gain in the solid. In this period important cytological and histological 

 changes are also going on in the soma cells of the body. The protoplasm be- 

 comes more watery and vacuoles appear, while cells become larger and more 

 turgid and the chromatic elements in the nuclei increase greatly in size and 

 stain deeply, thus presenting all the signs of intense activity. In general the 

 body on emergence passes through the same changes as those which are con- 

 nected with the preparation for hibernation, but in the reverse order. 



This process is a deep-seated one in decemlineata, and one that can not by 

 any known method be postponed or prevented. The process can be modified 

 in various ways, but it can not be eliminated from the life cycle of the species, 

 and, although through excessive and highly abnormal stimuli I have succeeded 

 in causing a semi-active hibernation, I have not been able by selection and 

 continued stimulation to modify this habit in the slightest. 



Hibernation has, in decemlineata at least, a decided selective influence which 

 acts to produce much the same result as does assortive mating. That is, a 

 very small number, if any, of the more extreme individuals of a population are 

 able to survive the hibernation period, and the most extreme of the variations 

 found in any generation in the autumn are almost certain not to emerge in the 

 following spring. In nature the second generation frequently contains a con- 

 siderable percentage of rather extreme individuals, so that the polygon of 

 variation is strongly skewed in one or the other direction ; but in the spring 

 the beetles which emerge from hibernation are not as strongly skewed, if at 

 all, which shows the leveling action of hibernation through the elimination of 

 extremes in variation. Just why these extreme variations should not be able 

 to survive the hibernation period is at present unexplained. The selective 

 influence of hibernation is well shown in the table on page 248. 



The selection produced through the elimination of the extremes during 

 hibernation is entirely in the direction of conservatism, tending to preserve 

 those individuals only which conform most exactly to the modal standard of 

 the species at a particular time and place. Hence, in the preservation of this 

 species and in the evolution of species in general, this selective influence would 

 act in precisely the same manner as does assortive mating. Likewise a large 



