46 THE DURATION OF LIFE. [I. 



following morning, with their wings fallen off, at the bottom of 

 their cage.' Dr. Speyer. 



Eupiihecia, sp. {Geometridae), ' when well-fed, live for three 

 to four weeks in confinement ; the males fertilize the females 

 frequently, and the latter continue to lay eggs when they 

 are very feeble, and are incapable of creeping or fljang.' Dr. 

 Speyer. 



The conclusions and speculations in the text seem to be suf^- 

 ciently supported from this short series of observations. There 

 remains, as we see, much to be done in this field, and it would 

 well repay a lepidopterist to undertake some exact observations 

 upon the length of life in different butterflies and moths, with 

 reference to the conditions of life — the mode of egg-laying, the 

 degeneracy of the wings, and of the external mouth-parts or 

 the closure of the mouth itself It would be well to ascertain 

 whether such closure does really take place, as it undoubted^ 

 does in certain plant-lice. 



VII. COLEOPTERA. 



Melolontha vulgaris. Cockchafers, which I kept in an airy 

 cage with fresh food and abundant moisture, did not in any 

 case live longer than thirty-nine days. One female only, out of 

 a total number of forty-nine, lived for this period ; a second 

 lived thirty-six da3's, a third thirty-five, and a fourth and fifth 

 twenty-four days ; all the rest died earlier. Of the males, only 

 one lived as long as twenty-nine days. These periods are less 

 by some days than the true maximum duration of life, for the 

 beetles were captured in the field, and had lived for at least 

 a day ; but the difference cannot be great, when we remember 

 that out of forty-nine beetles, only three females lived thirty- 

 five to thirty-nine days, and only one male twenty-nine days. 

 Those that died earlier had probably lived for some consi- 

 derable time before being caught. 



Exact experiments with pupae which have survived the 

 winter would show whether the female really lives for ten days 

 more than the male, or whether the results of my experiment 

 were merely accidental. I may add that coitus frequently took 

 place during the period of captivity. One pair, observed in 

 this condition on the 17th, separated in the evening ; they 

 paired again on the morning of the i8th, and separated in the 



