EN'TozoA. n: 



white deposit at the hottom of the excavation. It proved 

 to be an excellent material for cleaning and polishing plate; 

 and, on subsequent examination, under the microscope of an 

 Irish naturalist, was discovered to consist of fossil Infusoria.* 

 The accumulation of similar deposits is at present producing 

 important changes in the bed of the Nile, at Dongola in Nubia, 

 and in the Elbe at Cuxhaven; it is even choking up some of 

 the harbours in the Baltic sea.t 



When we consider the diminutive size of these creatures, 

 the stupendous monuments which they leave behind, and 

 the mighty changes which their unseen labours are silently 

 effecting, we must admit the justice of Ehrenberg's remark: 

 " Truly indeed the microscopic 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." 



Note.— May, 1854. A beautifully illustrated work, of great 

 scientific interest, has recently been published by the Rev. Wm. 

 Smith, on these minute shell-producing organisms (Diatomacece). 

 From this it appears that their mode of reproduction is 

 altogether of a vegetable character, analogous to that of the 

 Algoe, or water plants. According to these views, the organisms 

 by which the minute siliceous skeletons are produced should be 

 excluded from zoological works. The facts stated in former 

 editions respecting them are, however, allowed to remain, as 

 their value is not affected by any change of opinion respecting 

 the nature of the organisms by which they are deposited. 



Class ENTOZOA, or INTERNAL PARASITES. 



" Verily, for mine owne part, the more I looke into Nature's workes, 

 the sooner am I induced to beleeve of her, even those things that seem 

 incredible." — Holland's Plihy. 



The body of every vertebrate animal forttis the abode of 

 many other animals that live within it. These creatures con- 

 stitute the class Entozoa, a word which simply means " within 

 an animal," and is very appropriate to the internal parasites, 

 which constitute the present group. 



With this class we are as yet imperfectly acquainted; but 

 some idea of its numbers may be formed from the fact, that 

 no species of animal is supposed to be exempt from their 

 attacks, and that the human body is infested with no less 

 than eighteen species. It is stated that every animal has one 



• Drummond in Mag. Nat. Hist. 1839. 



t Ehrenberg in Edinburgh Phil Journal, vol. x.xxi. p. 386. 



