ROTIFERA. 39 



tacea, have utterly perislied. The discovery, therefore, by Ehrenberg, 

 of several, at least twenty, species, of silicious-shelled Infusoria, fossil, 

 in the chalk and chalk marls, which are perfectly identical with those 

 now living in the sands of the Baltic and North Sea, is a most interest- 

 ing addition to the obscure history of the introduction of the successive 

 species of animals on this planet, and must add greatly to the interest 

 of the Infusorial class in the eyes of the naturalist and geologist. 

 " For these animalcules," says Ehrenberg, " constitute a chain, which, 

 though in the individual it be microscopic, yet in the mass is a 

 mighty one, connecting the organic life of distant ages of the earth, 

 and proving that the dawn of the organic nature co-existent with us 

 reaches further back in the history of the earth than had hitherto 

 been suspected." 



The still existing species are by no means rare or isolated, but fill 

 in incalculable numbers the seas of Northern Europe, and are not 

 wanting on the tropical coasts of the globe. With reference to the 

 operations of the invisible Polygastria at the present day on these 

 and other coasts, I have only time to i*efer you to a paper by the 

 indefatigable Berlin Professor, entitled " Observations upon the im- 

 portant Part which Microscopic Organisms play in the choking up 

 of the Harbours of Wismar and Pillau ; also, in the Formation of the 

 Mud which is deposited in the Bed of the Elbe, at Cuxhaven, and 

 upon the agency of similar Phenomena in the Formation of the Bed 

 of the Nile, at Dongolar in Nubia and in the Delta of Egypt." 

 " Truly, indeed," says Ehrenberg, " the mici'oscopic organisms are 

 very inferior in individual energy to lions and elephants, but in their 

 united influences they are far more important than all these animals."* 



LECTURE III. 



ROTIFERA. 



The animal kingdom may be likened to a cone, the species of which 

 it is constituted diminishing in number as they ascend in the scale of 

 complexity. Rising from different parts of the basal circumference, 

 the different groups reciprocally approximate, interweaving their 

 mutual affinities within a progressively closer reticulation, until they 

 finally culminate in the apex, which is crowned by Man. 



* XXXn. p. 386. 

 D 4 



