SOI.LAS On (//> Origin of Freshwater Faunas. 



91 



state by winds, no inhabitant of freshwater streams ought to propagate, as a rule, 

 or exclusively by means of free-swimming larvae, for this would bo inconsistent 

 with its permanence as a freshwater form. I believe this deduction is capable of 

 being verified by facts. Before proceeding further it will be well to provide 

 ourselves with a list of known freshwater forms, and I have accordingly drawn 

 up the following Table of the Invertebrate sub-kingdom, and marked the various 



ups m. or/., according as they are freshwater or marine; an o after/, indicates 

 th:it the ^rnup is exclusively freshwater; an oJboforem. that it is exclusively marine; 

 f.m. indicates that it is both freshwater and marine. It will be observed that most 

 of the great groups are marked m.f. ; some, however, such as the Brachiopoda, 

 Ascidia, Kelmiodenuata, and other small outlying groups, Enteropneusta, Gephyrea, 

 ( 'hnctoirnatha, are wholly marine*. Those which are exclusively marine are not 

 further analvsed; but those which contain both freshwater and marine forms are 



Ueil step by stop into smaller and smaller groups, till a separation into exclu- 

 -i vely marine or exclusively freshwater forms is reached; or in case this does not 

 happen, till the families are divided into genera: beyond genera the subdivision 

 has not been carried ; but notes are added when a genus, otherwise exclusively 

 marine, presents us with some exceptional freshwater species. 



Monera, 



Protoplasta, 



Foraminifera, 



PKOTOZOA. 



/. m. 

 /. m. 

 o. m. (Gromia, /.) 



Radiolaria, 



Gregarinida, 



Infusoria, 



o. m. (Heliozoa, /.) 



f.m. 



f.m. 



METAZOA. 



Spongi;e, /. in. 



Ccelenterata, /. m. 

 Flatylielinintliia, / m. 



Rotifers, /. m. 



Brachiopoda, o. m. 



Polyzoa, /. m. 



(Jlia inpoda, f.m. 



Discophora, /. ///. 



Gephyi o. m. 



Chaetognatha, o. m. 



Nemathehninthia, /. m. 



Mollusca, /. m. 



Crustacea, /. m. 



Tracheata, /. m. 



Keliinodermata, o. m. 



Enteropneusta, o. m. 



Ascidia, o. m. 



Acraniota, o. m. 



* It may be at once observed here that in all tl f so groups propagation is accomplished by means of 

 free-swimmin . TLi.s fact sufficiently explains their entire absence from freshwater areas, and 



their wide distribution in the sea. 



