120 ENTOMOLOGICAL SOCIETY 



ation annually, and in which the larval life, being for the most part 

 predaceous and dependent upon Aphides, is greatly shortened, 

 while the life of the imago is prolonged, many of the species 

 living through the winter in this state. Thus, we have, again, in 

 the same family the two extremes. In the Platyptera we have in 

 the Termites or White Ants an illustration of the influence of the 

 social habit and organization on longevity very similar to that 

 w T hich we find among the social Hymenoptera ; for here, also, 

 while the workers are for the most part limited within the year 

 in their life duration, it is well known that some of the soldiers 

 live for a longer period, while the queens or fertile females live 

 for several years. So in the Bird-lice, or Mallophaga, the para 

 sitic habit has produced a distinct change, and we find species 

 breeding continuously upon our domestic animals and upon birds, 

 the limitation of individual life hard to define, but showing great 

 elasticity according to conditions. To some extent this is true of 

 the Psocidae, or at least of those species which are most frequently 

 met with around houses. It is well known that some of these 

 live for a long time in wainscoting, and, while no exact records 

 are at hand, there is every reason to conclude that development 

 is irregular, and that individual life may be abnormally prolonged 

 under conditions of low temperature and dryness. 



In the Plecoptera, or Stone-flies, we have an annual life quite sim 

 ilar to that of the other aquatic Neuroptera. Among the Epheme- 

 roptera, or May-flies, we have a most striking illustration of the 

 shortened existence of the adult, which, in some species, lasts for 

 but a few hours, and, in most, for but a few days. Finally, in 

 the Thysanura, w r e have no strict dividing Line between the 

 adults and the earlier stages, and the species have no regular 

 breeding periods. Many of them have a life not extending be 

 yond a few months, while others, as in Lepisma, doubtless, 

 occasionally survive more than one year. 



SPIDERS, TICKS, MITES. As to the spiders, Dr. Marx informs 

 me that he knows of no experimental facts of any consequence 

 bearing on their longevity. The same rules apply to them as to 

 the bulk of the Hexapods. The great majority of them are 

 limited in individual life to the single year and hibernate in the 

 egg state. The deviations, as in Hexapods, will be found in 

 those species which live in tunnels underground or have become 

 joint tenants with man in his abodes. The trap-door spiders 

 and some of the species which winter in our cellars often 

 extend individual life beyond the year. Like all predaceous 

 articulates, they have developed great sustaining power under 

 adverse food conditions. 



The same general conclusions may be applied to the Ticks, 



