470 WILSON. [Vol. XI. 



of nucleic acid and having (like chromatin) a special affinity for 

 the basic anilin dyes, the latter containing a lower proportion 

 of nucleic acid and having (like linin) a special affinity for the 

 acid anilins.^ From a strictly morphological point of view the 

 evidence is growing that chromatin may be directly or in- 

 directly converted into so-called cytoplasmic elements, as in 

 the formation of yolk-nuclei ^ of linin-fibres and spindle-fibres 

 as I have here described ; in the discharge of chromatin into 

 cytoplasm occurring in the formation of the polar bodies, or in 

 the periodic elimination of chromatin from the nucleus in the 

 development of Ascaris as described by Boveri. Without 

 denying the probability of true intra-cellular symbiosis in the 

 case of the chromatophores we may therefore with Biitschli 

 regard intra-cellular differentiation in general as the result of a 

 particular configuration of a continuous morphological structure. 

 There is no doubt that the morphological differentiation of 

 parts within the cell is accompanied by corresponding chemical 

 differentiations, and from a physiological point of view these 

 must in the long run be referred to local differences of meta- 

 bolic activity. This fact is most conspicuous in the case of 

 the nucleus (or chromosomes) and the chromatophores which 

 contain, and have the power of majiufactiiring, specific sub- 

 stances (nuclein, chlorophyll) of comparatively well-determined 

 composition. It is no less certain, as Heidenhain has insisted, 

 that the centrosome possesses a specific chemical composition 

 to which its remarkable effect on the cytoplasm must be due ; 

 and both in this case and that of the nucleus the chemical 

 nature of the organ undergoes periodic changes during the 

 cycle of cell-life as shown by regularly recurring changes in 

 staining reaction, such as those that have been described in the 

 present paper. From the physiological point of view, there- 

 fore, a "cell-organ" is a differentiated area of the cell-sub- 

 stance in which a specific form of chemical change occurs. 



1 See Lilienfeld, Ueber die Wahlverwandschaft gewisser Zellenelemente zu 

 Farbstoffen. Arch. Anat. u. Phys., Phys. Abth., 1893. Also, Zacharias, Ueber 

 Chromatophilie. Ber. d. Detitsch. Bot. Ges., 1893. 



2 See Calkins on the yolk-nucleus of Lumbricus. Trans. N. Y. Acad. Set., 

 June, 1895, ^^^ many earlier papers there cited. 



