80 A, A. Girault: 



continents remained unknown to others and were never visited. 

 Civilizations were restricted to a few centers, were not advanced and 

 the great majority of men were living in a state of savagery, roaming 

 from one part of a continent to another, keeping no plants and animals 

 under cultivation and therefore apparently having little or nothing 

 to do with the unconscious agency of transporting minute insects 

 from place to place. Occasionally, there must have been long mi- 

 grations of bodies of men, even from one continent to another perhaps 

 always through natural or accidental causes, certamly so at first. 

 These migrations seemingly could in no way have affected the dispersal 

 of Trichogrammatidae from one continent to another, since at the time 

 we have in mind men would scarcely have carrried anything in bulk 

 from one continent to another but must have depended upon such 

 food as would barely suffice for the journey, or that could be obtained 

 on the way; the journey in most cases would require a long period 

 of time. Nevertheless, our Imagination cannot help seeing possibilities 

 even here. Parts of plants with the stems and foliage attached would 

 have been carried along as food, perhaps, or eise fruits containing the 

 eggs of insects infested with trichogrammatids; or eise grasses might 

 have been carried along either for crude bedding or for some other 

 purpose. All of these could easily have happened. In the rapidity of 

 modern times it is a common experience for entomologists to send 

 fruit infested with the parasited eggs of an insect over long distances 

 with certainty that the parasites will survive; from one continent 

 to another this has been done by the use of cold storage and the know- 

 ledge of this last fact, opens still further the early possibilitie sof uncon- 

 scious dispersal by men foUowed by subsequent establishment of the 

 insects so dispersed; human migrations into temperate climates during 

 the winter for instance, accidental or otherwise. 



But thousands of centuries of years must already have elapsed 

 since the migrations of the ancestors of the existing species of different 

 portions of the earth and man, consequently, must have been in a 

 very low stage of development. Though, it must certainly be true 

 that even then he was migratory and may have had more or less 

 unconscious agency in the distribution of these and other forms of 

 life, yet it is equally, if not more probable, that other factors were 

 concerned in a greater degree. The dispersal of their hosts was one 

 of the factors of the greatest importance. The parasites followed their 

 hosts and at first probably did not extend beyond their habitat. How 

 the hosts became scattered would take too much space for discussion 

 here but the means are not unlike those for the parasites. These minute 

 insects fly and must at times be blown enormous distances by the 

 wind, as during gales and storms; females thus transported, being 

 parthenogenetic and adaptable, would in some cases at least, readily 

 find a host and then become established in a new region. This Operation 

 repeated Century after Century offers a likely explanation for dispersal 

 over continents and even adjoining Islands. The dispersal from con- 

 tinent to continent has already been explained. The mere fact that in our 



