56 



GENERAL HISTOEY OF 



Polj'-gastric Infusoria, and afterwards JRotataria." (Ed. Phil. Jour. 

 V. 23.) 



Sectiox XVII. — Of the affiyiities and classification of Polygastrie 

 Animalcules. — Our next business is to detenninc the affinities existing 

 between the Pohjgastrica and other animals and plants. 



Commencing- with the simplest ; life is seen so obscurely manifested, 

 that in many cases, we know not -SA'hether to esteem it vegetable or 

 animal, and the organisms of both kingdoms, in theii- earliest phase, 

 are, to common observation, identical. In such, there is no other 

 indiAddualization of organs than is necessaiy to form a centre of 

 generative or spermatic force — i. e. a nucleus, in which an energy, 

 originating, each half of the dividing nucleus becomes a centre of 

 assimilative force, and complete fission of the entire being is brought 

 about. Examples in Monodina, and in the vegetable Palmellea. 



The next stage in advance, shows so much of the special modifi- 

 cation of the general mass, as is necessary to the pi'oduction of cilia, 

 or of one or more filiform processes or proboscides. Many of the 

 monads aflbrd examples of this degree of development, which is yet 

 so rudimentary and ill defined, that there are no certain means of 

 distinguishing -n'hat arc specific, distinct animal existences, and what 

 but germs of plants, or the early stages of existence of other animals, 

 or of plants. Here again, therefore, aifinities are so close, as scarcely, 

 or not at all, to be separated from identities. 



This ciliated monadiform existence belongs to the spores of many 

 plants, and to embryonic conditions of most invertebrata, and, for 

 convenience, is spoken of by Professor Owen, (Op. cit.) as the 

 " Leueophiycan tj-jie." This type is witnessed in the developing 

 ova of the sponges, and of the Annelida; and there are sufficient 

 grounds for supposing its occurrence, in an early stage of existence, 

 of many of the more highly organized Infusoria. 



However, there is one caution to be borne in mind, in seeking for 

 the analogy between specific forms and embryonic phases, viz., not 

 to cjnfound general resemblance with specific idcntit3^ If it be not 

 discernible, we must assume (from what we know of the course of 

 development of higher animals) that there is something wanting in 

 th(! image, to render it an exact counterpart of the original. 



Uut we have to deal, not only with single monads, but with such 



