POLYGASTRIA. 37 



members of nature's invisible police are every where ready to arrest 

 the fugitive organised particles, and turn them back into the ascending 

 stream of animal life. Having converted the dead and decomposing 

 particles into their own living tissues, they themselves become the 

 food of larger Infusoria, as e. g. the Botifei^a, and of numerous other 

 small animals, which in their turn are devoured by larger animals, as 

 e. g. fishes ; and thus a pabulum, fit for the nourishment of the highest 

 organised beings, is brought back by a short route, from the extremity 

 of the realms of organic nature. 



There is no primordial and self-subsistent organic matter, as Buffon 

 taught : the inorganic elements into which the particles of organic 

 matter pass by their final decomposition are organically recomposed, 

 and fitted for the sustenance of animals, through the operations of 

 the vegetable kingdom. No animal can subsist on inorganic matter. 

 The vegetable kingdom thus stands, as it w^ere, in the breach between 

 animal matter and its ultimate destruction ; but in this great office 

 plants must derive most important assistance from the polygastric 

 Infusoria. These invisible animalcules may be compared, in the 

 great organic world, to the minute capillaries in the microcosm of the 

 animal body, receiving organic matter in its state of minutest sub- 

 division and when in full career to escape from the organic system, 

 and returning it by new channels towards the central and highest 

 point of that system. Like true beneficence, they work their good 

 unobtrusively and unseen. 



But besides the important functions which the Polygastria per- 

 form in relation to the conservation of organic matter and of the 

 purity of the atmosphere, they likewise take their share in modi- 

 fying the crust of the earth. It has been shown that some Poly- 

 gastria are naked, others loricated or defended by silicious shells, of 

 definite and easily recognisable forms and patterns in difi'erent 

 species. Professor Ehrenberg had not long made these observations 

 before he discovered that a certain kind of silicious stone, called 

 Tripoli or Polierschiefer, was entirely composed of such cases — 

 was, in fact, the debris of Polygastric animalcules, chiefly of an 

 extinct species, called Gaillonella distans. The substance alluded 

 to has long been known in the arts, being used in the form of 

 powder for polishing stones and metals. At Bilin, in Bohemia, there 

 is a single stratum of this substance, not less than fourteen feet thick, 

 forming the upper layer of a Tripoli hill, in every cubic inch of which 

 layer Ehrenberg estimates that there are forty-one thousand millions 

 of individuals of the Gaillonella distans. It likewise contains the 

 shells of NaviculcE, Bacillaria, Actinocyclus, and other silicious ani- 

 malcules. The lower part of the stratum consists of the skeletons of 



D 3 



