240 Dr. Max Weber on the 



assumption that the freshwater fauna of the earth has in part 

 a similar character, in so far as there are a whole number of 

 identical species, or at any rate genera, which are widely- 

 distributed over the world. I need but recall to mind many 

 Protozoa, Spongillidaj, Hydra, Hirudinea, Naidaj, Turbel- 

 laria, and various Bryozoa and Entomostraca. A common 

 characteristic of these forms, however, is smallness of body 

 and easy transportability occasioned thereby or by other 

 qualifications ; still more, however, such a constitution of 

 their germs that these can sustain changes of temperature and 

 drought, and by means of wind or other mode of conveyance 

 can be readily transferred from one freshwater station to 

 another. Pregnant instances of this are already recorded in 

 numbers in the writings of Darwin, Forel, Semper, and 

 Zacharias, and in the latest suggestive work of Simroth *, 

 and are known to everyone. It is enough to remind the 

 reader of encysted Protozoa which are carried away in the 

 mud on the feet of birds and also in their droppings ; or of 

 the shell-protected Qg^ of Hydra, which like Hydra itself is 

 easily transported. Species may also be carried by means of 

 leaves, which are caught up by the wind from a pool which 

 is drying up, as I observed in the ease of Spongillidae in 

 India. The gemmulffi of freshwater sponges are, as is well 

 known, especially fitted for such and similar modes of 

 transport ; this applies in quite a peculiar degree to those of 

 Spongilla deciinens, a species described by myself, the 

 numerous gemmulas of which, surrounded by tissue containing 

 air, float upon the water equally as well as the statoblasts of 

 Bryozoa, which I likewise met with in abundance in India. 

 All these germs, precisely like the " winter " eggs (Dauereier) 

 of the Cladocera in their ephippia, are driven or wafted to the 

 shore as they float upon the surface of the water, and are then 

 an easy sport of the winds or other transporting medium. 



It has only recently been shown by de Guerne f how Hiru- 

 dinea are carried by birds, while Blanchard \ and Megnin § 

 have pointed out that a similar result is also brought about by 

 mammals. 



All the species mentioned hitherto, which in one form or 

 another are readily transported, and for this reason alone, 

 apart from any other, may be more generally distributed over 

 the earth, we will term " universaV freshwater animals. 

 Besides these the freshwaters of the different districts contain 



* Simroth, '■ Eutsteliuu^ der Laudtbiere.' Leipzig, 1892. 

 t J. de Guerue, Comptes liendus liebd. d. 1. Soc. de Biologie, 1892, 

 p. 92 ; and Anu. Mag. Nat. Hist. ser. 6, vol. x. pp. 117-120. 

 X Blaucliard, Bull. Soc. Zool. de France, xvi. 1891, p. 218. 

 § MegTiiu, Bull. Soc. Zool. de France, xvi, 1891, p. 222. 



