PROTOZOA AM(EBA. 



405 



by the breaking up of its contents into several particles ; but 

 new cells are not unfrequently to be met with, especially in the 

 nutritive fluids of such Animals as possess a distinct circulation, 

 which have not directly originated in either of these modes from 

 a previously existing cell, but which have been developed by a 

 process of free cell-formation, namely, by the aggregation of 

 organic molecules, floating in these fluids, into little masses, of 

 which the external particles coalesce into a membranous cell- 

 wall, whilst the interior liquefy into cell- contents. This can 

 only take place, however, in a liquid which has undergone ela- 

 boration in the interior of a highly-organized living body ; and 

 we find no traces of such free cell-formation among the members 

 of the group we are first to investigate. 



261. As we have seen ( 150) that, among the lowest Proto- 

 phytes, the general attributes of a cell may exist in a minute 

 mass of protoplasm which is not bounded by a limitary mem- 

 brane, the differentiation between cell-wall and cell-contents 

 not having yet manifested itself, so, among the lowest Protozoa, 

 we find the power of maintaining an independent existence to 

 be possessed by similar particles of that peculiar blastema, or 

 formative substance, to which the name of sarcode has been 

 given by Dujardin (who first drew attention to its extraordinary 

 endowments), and which may be considered as the basis, not 

 merely of the entire organisms of Protozoa, but of a large part 

 of that of higher animals. The properties of this may be most 

 fully understood by the care'ful study of a creature, which is by 

 no means unfrequently to be met with in fresh and stagnant 

 waters, vegetable infusions, &c., and which, from the great 

 variety of forms it assumes, has received the designation of Pro- 



FIQ. 191. 







Amoeba princeps, in different forms, 



teus. This name, however, having been assigned to an animal 

 of far higher organization, that with which we are now con- 

 cerned is properly known as the Amoeba (Fig. 191). It may be 



