Fresh-water Entomostraca of South America. 



these little creatures in the living state, and to obtain 

 information about their different habits and their develop- 

 ment from generation to generation, each aquarium repre- 

 senting, as it were, an isolated part of their native dwelling 

 places. As, moreover, the different species pertaining to a 

 certain locality do not, as a rule, appear simultaneously, 

 but rather in a definite succession, any sample of plankton 

 taken occasionally will give a far less complete idea of the 

 fauna than a continuous series of hatching experiments insti- 

 tuted on a parcel of mud from the same locality. 



Besides the material kindly sent to me by Dr. v. Ihering 

 and taken in the neighbourhood of Sâo Paulo, Brazil, I have 

 received another sample of dried material from Argentina, 

 through the kind intervention of the Norwegian gentleman 

 Mr. Schiander. This material, consisting of dried aquatic 

 plants with adhering mud, proved to be extremely suitable 

 for hatching operations, and numerous interesting forms 

 were raised from it, some of which were identical with forms 

 reared from the Brazilian mud, whereas others represented 

 particular species. 



Among the several species derived from these 2 regions 

 of South America, there is a considerable number which 

 have proved to be common to both the new and the old 

 world, some even being identical with species found as far 

 north as Norway. Indeed, as will be shown in this paper, 

 the geographical distribution of some of the species appears 

 quite perplexing, and can scarcely be accounted for without 

 the assumption of a rather different relation between the 

 great continents and oceans in ancient times. 



A rather serious objection might perhaps be urged 

 against the reliability of these statements, as far as those 

 species, which are known to occur in Norway, are concerned. 



