1884.] 47 [Hyatt. 



The homology of a Protozoon with an isolated cell of the tis- 

 sues of any of the higher egg-bearing animals, or Metazoa rests 

 upon similarity in structure, and in the mode of performing the 

 essential functions of reproduction and assimilation. There are, 

 however, objections, which throw doubt upon the unicellular 

 character of the higher forms of the Protozoa. There are some 

 which like Actinophrys seem to be made up of cells, and others 

 among Flagellata and Ciliata having internal organs, and cer- 

 tainly a distinct integument, which has a cellular aspect. M. J. 

 Kunstler has written the ablest exposition of such views in an 

 article on Flagellata in Bull. Soc. Zool. de France, 1882, pt. 1. 



This author though adhering to the unicellular theory, denies 

 the usual assertion of the simplicity of the cell and adduces many 

 facts in favor of the opinion, that cells in the higher Protoza and 

 among Metazoa are not primitive morphological elements, but 

 may be composed of elementary discs, sarcous elements " sphe- 

 rules protoplasmiques." These views are developed from those 

 of Bowman, Milne Edwards and others, and are useful in enab- 

 ling us to account for the structures of the muscles in the higher 

 animals and seem also to be applicable to the explanation of the 

 differentiated integuments and organs of Flagellata and Ciliata. 



tozoon is also a unicellular zoon, a Metazoon also a multicellular zoon. The typical 

 sponge as we have defined it above is a Spongozoon. This use of a new word enables 

 us to avoid the confusion of Huxley, who allowed himself to be bound by the old term 

 and its common usage. He, therefore, was forced to regard the individual among ani- 

 mals as including, " the whole product of one egg," a definition admirably adarted to 

 man and single animals but inadmissible for the cycles of the invertebrates. This term 

 cannot express the cycle of hydra, colony, gonophore, or medusa, the latter both 

 males and females, and when separate capable of exercising all the functions and com- 

 pletely filling out the conventional idea of individuality. By using this new term on 

 the other hand the hydra may be conveniently designated as a Hydrozoon, the colony 

 a colony of Hydrozoons, the gonophore. or fully developed Medusa, and the bud or egg, 

 also Hydrozoons, in whatever shape they may appear. The egg is a zoon of the sim- 

 plest form and while still a single cell homologous with a Protozoon becoming a Meta- 

 zoon as soon as its character as a mass of tissue building zoons is apparent. The use 

 of the word individual also involves us in curious dilemmas, thus a Protozoon is an 

 individual but its homologue the single cell cannot be expressed by the same term 

 and certainly the attempt to stretch it in order to accomodate a colony as above de- 

 scribed, on the ground of the inseparability of the different forms, would oblige us log- 

 ically to call the whole biological cycle an individual. Metaphysically this may be 

 correct, but it neglects all morphological and definite boundaries in the use of termi- 

 nology, and is putting new wine into old bottles without regard to the possible con- 

 sequence. 



