48 THE DURATION OF LIFE. 



In addition to these cases, Dr. Hagen writes to me: 'Among the 

 beetles which live for more than a year, Blaps, Pasimachus, (Cara- 

 lidae] and among ants, almost thirty per cent, are found with the 

 cuticle worn out and cracked, and the powerful mandibles so greatly 

 worn down that species were formerly founded upon this point. 

 The mandibles are sometimes worn down to the hypodermis.' 



From the data before me I am inclined to believe that in certain 

 beetles the normal length of life extends over some years, and this 

 is especially the case with the Blapidae. It seems probable that in 

 these cases another factor is present, a vita minima, or apparent 

 death, a sinking of the vital processes to a minimum in consequence 

 of starvation, which we might call the hunger sleep, after the ana- 

 logy of winter sleep. The winter sleep is usually ascribed to cold 

 alone, and some insects certainly become so torpid that they appear 

 to be dead when the temperature is low. But cold does not affect 

 all insects in this way. Among bees, for example, the activity of 

 the insects diminishes to a marked extent at the beginning of 

 winter, but if the temperature continues to fall, they become active 

 again, run about, and as the bee-keepers say, ' try to warm them- 

 selves by exercise ' ; by this means they keep some life in them. 

 If the frost is very severe, they die. In the tropics the period of 

 hibernation for many animals coincides with the time of maximum 

 heat and drought. This shows that the organism can be brought 

 into the condition of a vita minima in various ways, and it would 

 not be at all remarkable if such a state were induced in certain in- 

 sects by hunger. Exact experiments however are the only means 

 by which such a suggestion can be tested, and I have already com- 

 menced a series of experiments. The fact that certain beetles live 

 without food for many years (even six) can hardly be explained on 

 any other supposition, for these insects consume a fair amount of 

 food under normal conditions, and it is inconceivable that they 

 could live for years without food, if the metabolism were carried on 

 with its usual energy. 



A very striking example, showing that longevity may be induced 

 by the lengthening of the period of reproductive activity, is com- 

 municated to me by Dr. Adler in the following note : ' Three years 

 ago I accidentally noticed that ovoviviparous development takes 

 place in Chrysomela varians, a fact which I afterwards discovered 

 had been already described by another entomologist. 



