THE CELL AND CELL DIVISION 81 



dicentric system. It is suggested, reasonably, that the chemical altera- 

 tion is such that the centrosomes absorb or condense the more liquid 

 parts of the cytoplasm, leaving this considerably more dense than in the 

 vegetative condition (Biitschli, Rhumbler). The existence of two such 

 centers withdrawing the more liquid parts of the cytoplasm would 

 lead to the radiations seen in the asters and spindle, which would thus re- 

 sult from a physical alteration of the structure of the cytoplasm induced 

 by the chemical changes within the centrosomes. This is all extremely 

 hypothetical of course, but there are many inorganic phenomena as 

 well as processes to be seen in the cleavage of the egg w T hich lend con- 

 siderable support here. At any rate these hypotheses represent the 

 state of our present ignorance of the nature and origin of the mitotic 

 figure and process. There are many reasons for believing that the chem- 

 ical differentiations within the cell are of fundamental importance here, 

 such as the fact that cells can be made to divide artificially by altering 

 their chemical structure. And that interactions of the nucleus and 

 cytoplasm are involved is indicated by the important observation that 

 while the amphiaster may be formed in the absence of a nucleus, no 

 real division of the cell may occur without the presence of nuclear 

 material (Boveri, Ziegler). 



REFERENCES TO LITERATURE 



VON BAER, K. E., Die Metamorphose des Eies der Batrachier vor der 

 Erscheinung des Embryo und Folgerungen aus ihr fur die Theorie 

 der Erzeugung. Arch. Anat. u. Phys. 1834. 



BALTZER, F., Zur Kenntnis der Mechanik der Kerntheilungsfiguren. 

 Arch. Entw.-Mech. 32. 1911. 



BENDA, C., Die Mitochondria. Ergebnisse Anat. u. Entw. 12. 1903 

 (1902). 



VAN BENEDEN, E., Recherches sur la composition et la signification de 

 Pceuf, etc. Mem. Acad. roy. Belgique. 34. 1870. Recherches 

 sur la maturation de Pceuf et la fecondation. Arch. Biol. 4. 

 1883. 



BONNEVIE, K., Chromosomenstudien. Arch. Zellf. 1. 1908. 



BOVERI, T., Zellenstudien II. Die Befruchtung und Teilung des Eies 

 von Ascaris megalocephala. Jena. Zeit. 22 (16). 1888. Zel- 

 lenstudien III. Ueber das Verhalten der chromatischen Kern- 

 substance bei der Bildung der Richtungskorper und bei der 

 Befruchtung. Jena. Zeit. 24 (17). 1890. Ueber die Befruch- 

 tungs- und Entwickelungsfahigkeit kernloser Seeigel-Eier, etc. 

 Arch. Entw.-Mech. 2. 1895. Zur Physiologic der Kern- und 

 Zelltheilung. Sitz.-Ber. Phys.-Med. Ges. Wtirzburg. 1897. 



