LIFE AND DEATH. 157 



moths, lay their egg's one after another and then die. The eggs of 

 the parthenogenetic PsycJudae are laid directly after the imago has 

 left the cocoon, and death ensues immediately, so that the whole life 

 of the imago only lasts for a few hours. No one could look upon 

 this brief life as a primitive arrangement among Lepidoptera, any 

 more than we do upon the absence of wings in the female Psychidae; 

 shortening of life here is therefore clearly explicable. 



In such cases have we any right to speak of the fatal effect of 

 reproduction ? We may certainly say that these insects die of 

 exhaustion ; their vital strength is used up in the last effort of 

 laying eggs, and in the case of the males, in the act of copulation. 

 Reproduction is here certainly the most apparent cause of death, N 

 but a more remote and deeper cause is to be found in the limita- 

 tion of vital strength to the length and the necessary duties of 

 the reproductive period. The fact that there are female Lepi- 

 doptera which, like the emperor -moths, do not feed in the 

 imago-state, proves the truth of this statement. They still 

 possess a mouth and a complete alimentary canal, but they have 

 no spiral ' tongue,' and do not take food of any kind, not even a 

 drop of water. They live in a torpid condition for days or weeks 

 until fertilization is accomplished, and then they lay their eggs and 

 die. The habit of extracting honey from flowers common to most 

 hawk-moths and butterflies would not have thus fallen into 

 disuse, if the store of nutriment, accumulated in the form of the fat- 

 bodies, during the life of the caterpillar, had not been exactly 

 sufficient to maintain life until the completion of oviposition. The 

 fact that the habit of taking food has been thus abandoned is a 

 proof that the duration of life beyond the reproductive period would 

 not be to the advantage of the species. 



The protraction of existence into old age among the higher 

 Metazoa proves that death is not a necessary consequence of repro- 

 duction. It seems to me that Gotte's statement ' that the 

 appearances of senility must not be regarded as the general cause 

 of death ' is not in opposition to my opinions but rather to those 

 which receive general acceptance. I have myself pointed out that 

 ' death is not always preceded by senility or a period of old 

 age V 



The materials are wanting for a comprehensive investigation of 

 1 See the first essay on ' The Duration of Life,' p. 21. 



