ZOOLOGICAL AFFINITIES. 90 



as known, in all the members of the Flagellata, the coalescing units are 

 frequently of diverse size and contour, the one larger and more rounded, and 

 the other smaller and more attenuate. The inference to be derived from this 

 circumstance, combined with the fact that in the conjugative process the 

 smaller unit mostly, if not invariably, becomes absorbed by or immersed 

 within the substance of the larger, is unavoidable. The larger unit takes the 

 place of the female element, and in itself figuratively and physiologically 

 represents the monocellular unimpregnated ovum ; the smaller one to an 

 equivalent degree is identical with the male element or spermatozoon, and 

 through its union with the female one communicates to the latter that re- 

 vivifying influence expressed through a capacity to prolong the reproductive 

 function, and whether that function takes the form of binary division, gem- 

 mation, or spore-production, the dioecious generative type may certainly 

 be said to be represented in its most elementary condition. With those 

 animalcules, on the other hand, such as Paramecium and Bursaria, in which 

 conjugation is simply transient and incomplete, and where both conjugative 

 factors meet and part on equal terms, both the male and female elements, 

 if such are represented, are necessarily united in each individual zooid, and 

 the generative system is as distinctly and essentially hermaphrodite or 

 monoecious. 



Affinities of the Infusoria to the Higher Zoological Groups. 



Among the very extensive, and in some respects heterogeneous, assem- 

 blages of animal forms associated in this volume under the comprehensive 

 title of the Infusoria there is necessarily encountered a series of races or 

 types that not only differ very widely from one another, but which occupy, 

 so far as it is possible to predicate, a very different rank or position with 

 relation to the outlying representatives of the organic series. Being ac- 

 cepted, as already explained, as simple unicellular organisms or Protozoa, 

 no comparisons possessing a homologic value can necessarily be instituted 

 between the Infusoria and any members of the more highly organized and 

 multicellular Metazoa. It remains, however, to be shown that, while no 

 such direct homological comparisons can be established, there permeates 

 throughout the ranks of this extensive group a substratum of superficial 

 or homoplastic resemblances whose existence it is impossible to ignore. 

 Regarded from this point of view, the Infusoria will be found, like an archi- 

 tect's puny and homogeneous clay or plaster model, to, as it were, anticipate 

 and pre-typify the elaborate edifice of multiple and diverse materials 

 afterwards erected or eliminated from this same" primary simple plan. 

 In yet another direction it is likewise capable of demonstration that 

 a very considerable number of infusorial animalcules foreshadow or typify 

 in a corresponding manner, in either their isolated or socially aggregated 

 condition, the separate or associated cellular elements out of which the 

 higher tissue-structures or Metazoic organisms are built up. The like- 

 ness in this last instance is necessarily far more substantial than in the 



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