328 SOME PROBLEMS OF CELL-ORGANIZATION 



while the intermediate terms are formed by the successive aggrega- 

 tion of these to form the chromatin-granules of which the dividing 

 chromosomes consist. Whether any or all of these bodies are *' indi- 

 viduals " is a question of words. The facts point, however, to the 

 conclusion that at the bottom of the series there must be masses that 

 cannot be further split up without loss of their characteristic proper- 

 ties, and which form the elementary morphological units of the nucleus. 

 In case of the cytoplasm the evidence is far less satisfactory. 

 Could Rabl's theory of fibrillar persistence, as developed by Heiden- 

 hain and Kostanecki, be established, we should indeed have almost a 

 demonstration of panmeristic division in the cytoplasm. At present, 

 however, the facts do not admit the acceptance of that theory, and 

 the division of the visible cytoplasmic granules must remain a quite 

 open question. Yet w^e should remember that the dividing plastids 

 of plant-cells are often very minute, and that in the centrosome we 

 have a body, no larger in many cases than a ** microsome," which is 

 positively known to be in some cases a persistent morphological ele- 

 ment, having the power of growth, division, and persistence in the 

 daughter-cells. Probably these powers of the centrosome would 

 never have been discovered were it not that its staining-capacity ren- 

 ders it conspicuous and its position at the focus of the astral rays 

 isolates it for observation. When we consider the analogy between 

 the centrosome and the basichromatin-grains, when we recall the 

 evidence that the latter graduate into the oxychromatin-granules, and 

 these in turn into the cytomicrosomes, we must admit that Brlicke's 

 cautious suggestion that the whole cell might be a congeries of self- 

 propagating units of a lower order is sufficiently supported by fact 

 to constitute a legitimate working hypothesis. 



LITERATURE. VI i 



Van Beneden. E. — (See List IV.) 



Van Beneden and Julin. — La segmentation chez les Ascidiens et ses rapports avec 



Torganisation de la larve : Arch. Biol.. V. 1884. 

 Boveri. Th. — Zellenstudien. (See List IV.) 



Briicke, C. — Die Elementarorganismen : lVie?ier Silz.-Ber., XIAV. 1861. 

 Biitschli, 0. — Protoplasma. (See List I.) 

 Delage. Yves. — La structure du protoplasma, et les theories sur Theredite. Parts, 



1895. .. 

 Hacker. V. — Uber den heutigen Stand der Centrosomenfrage : Vcrh. d. deutsch. 



Zo'dl. Ges. 1894. 

 Heidenhain, M. — (See List I.) 

 Herla. V. — Etude des variations de la mitose chez Pascaride megalocephale : Arch. 



Biol.yAW. 1893. 



1 See also Literature, I., II., IV., V. 



