160 



PSYCHE. 



[February, 1901 



Josef Land, Nova Zembla, Siberia and 

 Alaska are found many of the species 

 common to Europe and the United 

 States, for example, Ah'anura imisavu/n, 

 Amirida gninaria, Achonitcs annafiis. 

 Isotoma palustris and viridis. Hitherto, 

 Totnocerus iiigcr of Europe, T. arctkiis 

 of Siberia and 7". americaiiHs of Cali- 

 fornia have been regarded as distinct 

 species. The Harriman expedition, 

 however, brought from Alaska numerous 

 specimens which form perfect inter- 

 gradations between the three forms 

 named. 



There is, then, not only a remarkable 

 agreement in structure between European 

 and North American CoUembola. but 

 also, for many species, continuity of dis- 

 tribution. 



The specific identity of so many Hol- 

 arctic species, an identity which would 

 not be expected upon a priori grounds, 

 may easily be accounted for. The 

 CoUembola and Thysanura, the most 

 generalized of iiexapods, present very 

 few adaptive characters as contrasted 

 with other insects. The CoUembola 

 feed upon organic debris and are mostly 

 confined to moist and decaying vegetable 

 matter or to water surfaces. Like the 

 worms, the simplicity of their e.xternal 

 organization is to be attributed to the 

 uniformity of their en\ironment. The 

 simple conditions of food, moisture, 

 temperature, etc., which a Collembolan 

 requires, may be found almost anywhere 

 in the Holarctic region ; .so that, after all. 

 it is difficult to understand how, under 

 such circumstances, any decided modi- 



fication of even varietal value could 

 occur. The species of continuous Hol- 

 arctic distribution are, in every case, only 

 such as can exi.st in a comparatively 

 simple environment, — the more spe- 

 cialized species and genera are not found 

 to any extent in the arctic region. 



The wide distribution of CoUembola 

 is surprising, for they appear to have no 

 means of self dispersal ; they lack wings 

 and probably always did, as none are 

 found in the embryo ; their feeble walk- 

 ing and leaping could procure only a 

 limited local distribution ; a dry spot is 

 an effective barrier to most CoUem- 

 bola, which require an atmosphere sat- 

 urated with moisture. The insects may 

 possibly be blown about to some extent, 

 but their eggs are probably not, as they 

 are laid in the soil, under bark, or in other 

 concealed places. 



As for accidental means of dispersal, 

 there may be many. Several species 

 not indigenous have been found in green- 

 houses among exotic plants. Isoioma 

 fimctaria, abundant in rich soil, fre- 

 quently occurs on potted plants. I used 

 to find Eutoiiiobrya iniiltifasciata and 

 other species among early strawberries 

 which had been brought to Massachu- 

 setts from the south. The influence of 

 man, then, in transporting CoUembola 

 upon plants, fruits or vegetables is not 

 inconsiderable. 



The lower animals perhaps assist now 

 and then. Moniez found a species of 

 Entomobrya by hundreds in the fresh 

 nesl of a linch, where they were feeding 

 upon the lining of feathers ; Wahlgren 



