IKFUSOEIAL ANIMALCULES. 65 



elaborate paper entitled " Passatstaub und Blutregen," (folio, 1849, 

 Berlin,) is presented a complete history of the showers of meteoric 

 dust, &c., which are on record, and the microscopic analysis of the 

 various specimens which he has procured. 



It happens with the Polygastrica, as with all other classes of 

 organized beings, that some families and genera are much more 

 widely diffused, and of more common occurrence than others. Every- 

 where, where there is decomposing organic matter in water, Vibriom'a, 

 Monadina, and Lemophrys, will be found. Examples of the genera 

 Vorticella, Vblvox, Paramecmm, Kolj)oda, Oxytriclm, and Euplotes, &e., 

 are common in ponds and strcams at all parts of the world, and often 

 in great numbers. Equally widely diffused are the two sections of 

 the family Bacillaria — Besmidiem and Diatomacece, the latter is pro- 

 minently cosmopolitan, and, in the abundance of its members, unsur- 

 passed. (See Part III.) Of the last section, the richest genera are 

 Eunotia, Navicula, Stirirella, Pinnularia, Gomphonema, Cocconeis, 

 Stauroneis, Actinoeyelus, Gallmiella, Bictyocha, Synedra, Coscinodiscus, 

 and Schizonema. 



We have several times alluded to the abundance of fossil Diatomacea, 

 which sometimes constitute the almost sole ingredient of masses of 

 rock or earth ; as, in the mountain meal {Berg-mehl) ; in various 

 polishing powders ; in the piire siliceous sand employed in the manu- 

 facture of porcelain, &c. And, inasmuch as any particular fossil 

 deposit, generally, possesses some peculiar species, or a particular 

 collection of species, it has happened that the antiquaiian has been 

 able to determine, that various ancient articles of pottery have been 

 made from the particular layer of clay in their vicinity, or, other- 

 wise, have been brought from a distance. 



Section XIX. — Of the Rotatoria as a class, and of their habits 

 and movements. — This tribe of beings possesses so complete an organi- 

 zation, that in a correct arrangement of the animal kingdom, it 

 would take its station far above many others, whose members are of 

 much larger magnitude. 



The comparatively large size of the Rotatoria, and the transparency 

 of their integument, have enabled the microscopic observer to ascer- 

 tain with certainty, in many cases, every part of their internal 



