Sorttas—On the 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 larvee, for this would be 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 
groups m. or f., according as they are freshwater or marine; an 0 after f. indicates 
that the group is exclusively freshwater; an o before m. 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, Echinodermata, and other small outlying groups, Enteropneusta, Gephyrea, 
Cheetognatha, are wholly marine*. Those which are exclusively marine are not 
further analysed; but those which contain both freshwater and marine forms are 
resolved step by step into smaller and smaller groups, till a separation into exclu- 
sively 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. 
PROTOZOA. 
Monera, f.™. | Radiolaria, o. m. (Heliozoa, /.) 
Protoplasta, fm. | Gregarinida, fm. 
Foraminifera, o. m. (Gromia, f.) | Infusoria, Sf. m. 
MeETAzoA. 
Spongie, f.m. Cheetognatha, 0. Mm. 
Coelenterata, fm. Nemathelminthia, t.m. 
Platyhelminthia, fm. Mollusca, fim. 
Rotifera, ff. m. Crustacea, fm. 
Brachiopoda, 0. Mm. Tracheata, fm. 
Polyzoa, f.m. Echinodermata, 0. M. 
Cheetopoda, fim. Enteropneusta, 0. mM. 
Discophora, fiom. Ascidia, 0. m. 
Gephyrea, 0. m. | Acraniota, 0.m. 
* It may be at once observed here that in all these groups propagation is accomplished by means of 
free-swimming larve. This fact sufficiently explains their entire absence from freshwater areas, and 
their wide distribution in the sea. 
