46 THE DURATION OF LIFE. 



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 undoubtedly 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 days, 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 cap- 

 tured in the field, and had lived for at least a day ; but the differ- 

 ence 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 considerable 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 1 7th, separa'ted in the evening ; they paired again on the 

 morning of the i8th, and separated in the middle of the day. 

 Coitus took place between another pair on the 22nd, and again on 

 the 26th. 



I watched the gradual approach of death in many individuals : 

 some days before it ensued, the insects became sluggish, ceased to 

 fly and to eat, and only crept a little way off when disturbed : they 

 then fell to the ground and remained motionless, apparently dead, 

 but moved their legs when irritated, and sometimes automatically. 

 Death came on gradually and imperceptibly; from time to time 

 there was a slow movement of the legs, and at last, after some 

 hours, all signs of life ceased. 



In One case only I found bacteria present in great numbers in 

 the blood and tissues ; in the other individuals which had recently 



