104 CYTOKINESIS. 



Meves ('96), in the spermatogonia and spermatocytes of the salamander, finds 

 the center close under the cell wall in the anaphase ; in the case of the smaller 

 spermatogonia and spermatocytes the centers move from this position through an 

 angle of 45° to 135°; in the larger spermatogonia no lateral movement takes place, 

 but only a movement toward the equator in the spindle axis, which is probably 

 caused by the contraction of the earlier spindle fibres. Meves believes that the 

 lateral movements of the centers in the smaller cells are caused by the development 

 of large and numerous astral rays on the side from which the centers move, which 

 rays serve to push the centers into their new positions. These movements do not 

 take place in a definite direction nor are they in the same plane in the two daughter 

 cells. In the eggs which I have studied this movement cannot be caused, as Meves 

 assumes, by the pushing of polar rays -on the side from which the centers move, for 

 in these eggs the whole cell contents rotate, as has been described. 



Montgomery ('98) has observed in the testis cells of Pentatoma that the new 

 centrosome appears at a point in the cell about 180° from that occupied by the old 

 centrosome. He has also observed that the idiozome material moves from the poles 

 to the equator of the dividing cell. 



(c) Ova and Blastomeres. — Mark ('81) first observed and figured a bent spindle 

 axis in the egg of Limax (see his figs. 91 and 93, in which the middle of the spindle 

 is shown displaced toward the center of the egg). MacFarland ('97) has shown the 

 same thing in one of his figures of Pleurophylidia (fig. 20), though he figures the 

 centrosomes as lying below the level of the nuclei, a thing which I have never ob- 

 served in any mollusk. 



Kostanecki ('97) says that in the cleavage of Physa the daughter cells take 

 opposite positions in the telophase while they turn against the spindle axis through 

 an angle of as much as 90.° The Zwischenkorper does not, therefore, lie in the 

 middle of the equatorial constriction, but is shoved to one side. 



Quite recently Rhumbler (1901) has described a periodic movement of the nu- 

 cleus to the cell surface within the living blastomeres of certain nematodes. At the 

 close of each cell division the nuclei migrate to certain places on the cell surface, 

 which places lie in the plane of cleavage of the following cell division. Between 

 the nucleus and cell surface Rhumbler has observed a clear area which he calls 

 the " Polfontaine," and which probably corresponds to the sphere of Crepidula. 

 The movements observed by Rhumbler entirely correspond to the movements in 

 telokinesis which I had previously described ('99) though he has evidently over- 

 looked my paper on this subject. 



Zur Strassen (1901) also has recently described the position of the centrosome 

 in the resting cells of Ascaris megalocephala. In brief, he finds that during the 

 resting period the centrosomes lie close to the cell surface, and he describes in detail 

 the symmetrical movement of the centrosomes and spheres toward the division plane 

 between two daughter cells. This movement in every respect resembles the move- 

 ments in telokinesis which I have described, and applies to the nuclei as well as to 

 spheres. Zur Strassen further finds that the form of each cell changes with the 



