OF WASHINGTON. 119 



Bat-flies have come under my notice, but we are justified in in 

 ferring that, just as in the case of the fleas, they are, under con 

 ditions adverse to development, capable of surviving for a much 

 longer period than are the non-parasitic families. 



ORTHOPTERA. What Weismann records under this order (in 

 which he includes Termes, Ephemeridae, Libellula, and Lepisma) 

 of Gryllotalpa, Gryllus, Locusta, and Acridium, is essentially 

 true of the Order as a whole, namely, that the species are annual, 

 existing on the average about half the year in the active condi 

 tion, maturing the latter part of the growing season, and perishing 

 soon after the eggs are laid or upon the approach of winter. As 

 I have expressed it in treating of Caloptenus spretus, they are 

 born with the coming of the leaves in spring and perish with 

 their fall in autumn. The Acrididaa, for the most part, hibernate 

 in the egg state. Yet there are numerous exceptions, and we 

 may have, in the very same region and under like conditions, 

 eggs laid early in the growing season and hatching in midsum 

 mer, and the mature insect developing in autumn and passing the 

 winter in a more or less active condition, as in Acridium ameri- 

 canum ; or we may have them hibernating in different stages of 

 development as larvae or pupae, as in the numerous species of 

 Tettix and in the Stenobothri. 



Among the crickets the species are for the most part single- 

 brooded, and those which live in the ground hibernate in various 

 stages of development, while tree crickets invariably pass the 

 winter in the egg state, and, together with the Mantes and Walk 

 ing-sticks, with the Locusts, Grasshoppers, and Katydids, hatch 

 in spring and perish in autumn. The Cockroaches, on the con 

 trary, which so frequently breed in and around human habitations, 

 show less regularity in development, and are more or less active 

 throughout the year, with a longer individual life-period than in 

 any of the other sections. In the sub-order Dermaptera, or Ear 

 wigs, we have, again, creatures which are fond of breeding near 

 human habitations, and the adult is known to live for the best part 

 of the year, but normally not to extend beyond the year. 



NEUROPTERA. Considering this old Order by its more modern 

 sub-divisions, it may be said that in the Odonata the larval life 

 is the essential part of the life of the individual. Among the 

 Dragon-flies none of the species hibernate in the adult state, and 

 most of them have an adult existence of but a few weeks, or at 

 most two or three months, living for the rest of the year, more or 

 less actively, as larvae in the water. The same is true of the 

 Trichoptera, or Caddis-flies, also of the Neuroptera proper, as 

 exhibited in the Ant-lions and Mantispas. In the Hemerobiidae, on 

 the contrary, we have species which produce more than one gener- 



