ON THE XATURE OF CELL-ORGANIZATIOX. 91 



give rise to a third organisui in ivhich each of them serves as 

 an orgaji to the zvhoie. 



It is needless to say that almost all structures in higher 

 organisms ^ are derived by the differentiation of some pre- 

 existing germ, but at the same time it is important to bear in 

 mind that this is not always the case, particularly in the lower 

 forms. It is this consideration which interests us particularly, 

 as it may be the key to the interpretation of the organization 

 represented by the single nucleated cell. 



III. 



The permanent organs of the cell are, following the recent 

 exposition of Strasburger,- considered to be (i) Cytoplasm, 

 (2) Nucleus, (3) Centrosome, (4) Chromatophore. 



The last named structure occurs normally in the cells of 

 green plants, and sometimes in those of animals.^ Following 



1 If Riickert's observation [Ubcr physiologischc Poly sperm ic bci incrohlastischen 

 Wirbeltiereiern, Anat. Anzeiger, Bd. VII, 1892) that in a certain vertebrate the 

 merocyte-nuclei come from the nuclei of the supernumerary sperm-cells which 

 enter the ovum, be confirmed, it would seem that a part of one important 

 embryonic organ, in an organism like Torpedo, is bodily derived from the outside 

 source. 



■■^ E. Strasburger : Das Protoplasnia lutd die Reizbarkeit, 1S91, Jena. 



^ See in this connection, Lankester's article Animal Chlorophyll (Xature, vol. 44, 

 1891) which is the review of G. Haberlandt's paper Ueber den Ban und die Beden- 

 tung der Chlorophyllzellen von Convoliita Roscoffensis, in von Graff's Die Organi- 

 sation der Tnrbellaria aeada, 1S91, Leipzig. I have not been able to see 

 Haberlandt's original paper. Haberlandt suggests, to quote Prof. Lankester, 

 "that while phylogenetically they [chlorophyll-cells in Convolnfa] must be regarded 

 as Algee (that is to say, have descended from Algae) yet at the present time they 

 have by profound adaptation to life in and with the Convolnta, altogether lost 

 their character as algal organisms, and have become an integral histological 

 element of the worm, and in fact constitute its assimilation tissue. . . . Haber- 

 landt is inclined to place his theory as to the green cells of Convoliita alongside 

 the suggestion of Schimper as to the origin of the chlorophyll corpuscles of higher 

 plant — namely, that these are due to the union in the remote past of a green 

 colored with a colorless organism." 



Schimper has shown that the chromatophores (Schimper's plastids) are formed 

 by the division of the preexisting chromatophores, and not by the differentiation 

 of the cell-protoplasm. .Schimper's view referred to above on the origin of the 

 chlorophyll bodies in the plant cells may be gathered from the following quota- 

 tions : " Sollte es sich definitiv bestatigen," says Schimper, " dass die Plastiden in 

 den luzellen nicht neu gebildet werden, so wurde ihre Beziehung zu dem sie 

 enthaltenden Organismus einigermassen an eine Symbiose erinnern. Moglicher- 



