288 Sketch of the Infusoria of the family Badllaria. 



The fluviatile species may be found in every pond, stream, 

 rivulet, bog, or pool, either nestUng among Confervac, parasitic on 

 aquatic plants, or living in the sedimentary matter at the bottom. 

 They often occur in such vast quantities as to cover hundreds of 

 square yards, to which they give a peculiar color — green, yellow- 

 ish or ferruginous, according to the peculiar internal coloring mat- 

 ter of the individuals. Most of the species are exceedingly mi- 

 nute, many are entirely invisible to the naked eye ; others, how- 

 ever, are quite perceptible without the aid of the microscope. 

 Notwithstanding their extreme minuteness, it is evident, from 

 their vast abundance, that they have some important offices to 

 perform in the economy of nature ; and like the coral insect, al- 

 though the individuals are minute, the result of their united la- 

 bors is on a scale by no means insignificant. 



Few organic bodies exceed in beauty the symmetrical, ele- 

 gantly sculptured forms of many of the species. Their beauty, 

 the singular phenomena they present, and the interest they have 

 lately received from being detected in a fossil state in Europe and 

 America, will be sufficient inducement for all lovers of micro- 

 scopic research to study this family. 



I shall now proceed to describe the most interesting American 

 species, commencing with the 



DESMIDIACEA. 

 Desmidium, 



Free, carapace simple, urceolate, trilateral, often catenate. — 

 Mandl. and Ehrenherg, I. c. p. 244. 



1. Desmidium Schwartzii. Ag. (PI. l,fig. 1.) " Corpuscles smooth, 

 quadrangular on three sides, slightly emargmate, triangular on the other 

 two sides, end obtuse, ovarium green, -g-V to ^^ of Paris line." 



The corpuscles of this species are united together by their tri- 

 angular faces, so as to produce long triangular (often twisted) fil- 

 aments, which are of a beautiful green color, and exceedingly 

 lubricous. Each filament is enveloped in a very transparent ge- 

 latinous matter, which is not visible on the dead specimens. The 

 filaments often occur together in great quantities, and form a stra- 

 tum in the water which is not distinguishable from a mass of 

 some species of Zygnema, with which remarkable genus of Al- 

 gae, this presents many points of resemblance. Allusion is made 



