CYTOKINESIS. 103 



R. Hertwig ('99) has seen a similar phenomenon in Actinosphcerium. He says, 

 p. 692, " Ehe die Theilung zu ende gefuhrt ist, wird die Spindelkorper bei der typ- 

 ischen Karyokinese der Actinosphserium liber eine Seite gebogen, so das die Toch- 

 terkerne spater dicht bei einander liegen (taf. Ill, figs. 10, 11) oder er wird bei clem 

 Eichtungstheilungen fast rechtwinkelig eingeknickt (taf. V, figs. 15, 16)." 



(b) Tissue Cells and Testis Cells. — M. Heidenhain ('94) in his great work on 

 the centrosome first described in detail the bending of the spindle axis and the 

 movements of the centrosomes and nuclei at the close of division. These move- 

 ments he designated " Telokinesis " and he properly recognized that they constitute 

 the final stage of cell division to which he gave the name "Telophase." 1 These 

 movements were observed in leucocytes and one-layered ejDithelium, and Heidenhain 

 supposed that they might be present in the division of many other cells. According 

 to Heidenhain the movements of the microcenter take place in a curve parallel to 

 the surface of the cell, while the nucleus probably moves in the reverse direction. 

 In one-layered epithelium the axis which passes through the microcenter and nu- 

 cleus, i. e., the cell axis, moves through an angle of 90° after each division; in em- 

 bryonic development it moves through varying angles. The result of these move- 

 ments is to bring the microcenter to the center of the cell and the nucleus to a 

 peripheral position. Heidenhain was unable to determine whether in these move- 

 ments the nucleus rotates so as to preserve its inner polarity. The cause of these 

 movements he finds in the contraction and expansion (Spannu-ng) of the organic 

 radii, i. e., through a lengthening of the polar group of radii and a shortening of the 

 radii which stretch over the nucleus to the opposite side of the cell. 



Erlanger ('96) found in the division of the branchial epithelial cells of the 

 salamander that the daughter cells regularly turn through an angle of 90° or more 

 toward the spindle axis of the mother cell. 



Similar movements have been observed in testis cells by Meves ('94, '96), 

 Moore ('95), and Prenant ('95). The latter has seen extensive movements of the 

 microcenter in the telophase of the testis cells of Scolopendra. The microcenters 

 of the two daughter cells are inversely symmetrical with reference to the axis which 

 joins the nuclei, the one being situated to the right the other to the left of that axis. 

 In some cases, however, the microcenters lie on the same side of the axis, i. e., the 

 symmetry is not inverse. Remnants of the spindle remain as a " perinuclear band," 

 which, he thinks, may be the agent of the movements of the microcenters. He does 

 not agree with Heidenhain that the microcenter lies in the center of the cell during 

 the rest, and this is certainly not true of the mollusks which I have studied. 



In the spermatocytes of elasmobranchs Moore finds that the centrosome, sur- 

 rounded by archoplasm, wanders toward the equator, and when it has reached a 

 point between the pole and the equator it moves to the cell periphery ; the centro- 

 some here lies between the chief mass of archoplasm and the cell wall. 



1 The custom of using this term to designate the final stages of the anaphase {cf. Wilson '96 and 

 1900, Coe '99, Griffin '99, et al) is to be deprecated, since Heidenhain's definition of this term is per- 

 fectly explicit and the stage to which it applies is clearly marked off from the anaphase. 



