2/8 THE PROTOZOA 



division-centre comes into direct contact with the chromatin, and is, 

 in part at least, surrounded by it. 



The facts point toward the conclusion that the centre of activity in 

 the division of the protozoan cell, as in Metazoa, resides in a special 

 structure, which, to avoid confusion in terminology, has been called 

 the division-centre. In some cases this structure resembles the astral 

 system of Metazoa, in consisting of an outer spherical mass with radi- 

 ating processes (astrosphere), and an inner focal granule or granules 

 (centrosome). The evidence further tends to show that the division- 

 centre in Protozoa consists of a specific substance different from the 

 chromatin and from the cytoplasm, and possessing above all other 

 portions of the cell an active role in division. No conclusive evidence 

 is forthcoming to show whether this substance is permanent in all 

 cells, or whether it was originally nuclear or cytoplasmic in origin, 

 although the widespread intra-nuclear condition favors the view that 

 it originated there. 



The origin of the central granule (centrosome or centriole) within 

 the division-centre is even more uncertain ; the few data at hand 

 lead us provisionally to believe with Balbiani and Hertwig that it is 

 derived from the chromatin. The observations, however, upon which 

 this conclusion is based are scanty, and further research must be 

 undertaken before we can hope for a sufficient basis of facts upon 

 which to generalize. 



SPECIAL BIBLIOGRAPHY VIII 



Boveri, T. Zellenstudien. Jenaische Zeitschrift, XXII . and XXIV., 1888 and 1890, 



and Part IV., 1901. 

 Brauer, Aug. Ueber die Encystierung von Actinosphaerium Eich. Z. w. Z., 



LVIII., 1894. 

 Biitschli, 0. Ueber die so-genannten Central-korper der Zelle und ihre Bedeu- 



tung. Vehr. d. Nat. Med. Ver. z. Heidelberg, N. F., IV., pp. 535-538, 1892. 

 Calkins, G. N. The Phylogenetic Significance of Certain Protozoan Nuclei. Ann. 



N. Y. Acad. Sciences, XI., 1898. 

 Hertwig, R. Ueber Kerntheilung, Richtungskb'rperbildung und Befruchtung von 



Actinosphaerium Eich. Abh. d. K. bay. Akad. d. Wiss. Miinchen, II. Kl. 



XIX., 1898. 

 Ishikawa, C. Ueber die Kerntheilung bei Noctiluca miliaris. Ber. Naturf. Ges. 



Freiburg, VIII., 1893. 

 Schaudinn, F. Ueber die Centralkorn der Heliozoen, eine Beitrag zur Centrosomen- 



frage. Verh. d. deutsch. Zool. Gesell., 1896. 

 Strasburger, E. Histologische Beitrage. IV., Jena, 1892. 

 Wilson, E. B. The Cell in Inheritance and Development, id Edition, New York, 



1900. 



