262 PROF. ALLMAN ON THE EECENT BESEAKCHES 



included the whole of the organisms we are here about to consider 

 in his group of Peotista, which he regards as composed of 

 beings which are neither animals nor plants, and which thus form 

 a third organic kingdom equivalent to the animal kingdom on one 

 side, and to the vegetable on the other. 



The advances which have of late years been made in our know- 

 letlge of the lowest forms of living beings are largely due to the 

 important reform introduced by Max Schultze into the theory of 

 the cell, when, by his researches on the Monothalamian Ehizopod 

 Cornuspira *, the old conception of the cell as a membranous sac 

 with contents gave place to the doctrine that in its original con- 

 dition the cell represents only a naked lump of protoplasm with 

 an imbedded nucleus ; and this doctrine gained further signifi- 

 cance when he insisted on the fact, of fundamental importance in 

 Biology, that the soft substance of the Ehizopoda, to which Du- 

 jardin had given the name of sarcode, was identical with the cell 

 protoplasm of all higher animals and plants. 



It was further shown by Haeckel f that there exists a great 

 number of the lowest orga^nisms whose structure is even simpler 

 than had been imagined by Max Schultze ; for in their naked 

 protoplasmic bodies there is never to be found at any period of 

 their lives a trace of a nucleus. He regards the nucleus as an 

 essential constituent of the genuine" cell," which he views as the 

 more highly developed elementary organism, and which ought 

 to be carefully distinguished from the lower homogeneous, non- 

 nucleated protoplasm mass, for which he proposes the name of 

 •' Cytode." 



Both these forms of elementary organisms (the cell and the 

 cytode) he embraces under the name of " Plastid," as being the 

 builders-up of all complex organisms. 



He regards this distinction of the two kinds of plastids as of 

 the greatest importance in its bearing on the phylogenetic or 

 genealogical history of organisms, since it is only such absolutely 

 simple organisms as cytodes that can originate by spontaneous 

 generation ( TTrzeugung), while it is only later on in the course of 

 the development that cells become evolved from the cytodes by 

 differentiation of an inner nucleus and an outer protoplasm. 



In the greatest number of organisms the individuals take their 



* " Ueber Cornuspira" Archiv fiir Naturg. 1860. 



t ' Generelle Morphologic ; ' and " Beitrage zur Plastidentheorie," Jenaieche 

 Zeitschr. vol. v. 



