PROTOPLASMIC MOVEMENT. 77 



What brings the germ nuclei and asters together ? In a 

 former lecture I suggested that the nuclei were passively drawn 

 together by the formation, attachment, and contraction of 

 astral rays. Wilson ('95) regards this view as untenable, and 

 concludes that " the nuclei are drawn together by an actual 

 attraction which is neutralized by union, and their movements 

 are not improbably of a chemotactic character." Unless the 

 nuclei have organs of locomotion it must still be true that they 

 are brought together by something outside themselves. This 

 something must of necessity be found in the cytoplasm (includ- 

 ing the aster), unless the nuclei are able of themselves to move 

 actively. I presume that amoeboid movement of the nucleus 

 would be the only kind possible, and yet I have never seen a 

 single case in which either of the germ nuclei was amoeboid. 

 There is every evidence that the nuclei in this, as in most other 

 cases of movement, are passive, and that their movements are 

 brought about by the activity of the cytoplasm. 



The migration of the sperm nucleus, like that of the matura- 

 tion spindles, is accompanied by progressive separation of yolk 

 and cytoplasm, and it is probable that these coincident phe- 

 nomena have a common cause in general movements of the 

 cytoplasm. 



Furthermore, there are certain elements of constancy in the 

 polar differentiation and in the plane of the first cleavage which 

 cannot be attributed to the nuclei, and, so far as I can see, can 

 be due only to definite characters of the cell body. It is the 

 egg cell and not the nuclei which shows polar differentiation. 

 The sperm nucleus and aster approach the animal pole from 

 various positions ; there is great variation in all the positions of 

 the nuclei and asters relative to each other, and yet there is no 

 variation in the plane of the first cleavage which always passes 

 through the point of extrusion of the polar bodies, and in cases 

 where the first cleavage is unequal the mitotic figure is always 

 eccentric to the same degree. Now the first cleavage, as we 

 shall see, is accompanied by extensive rotary movements of the 

 cell contents, and this fact, joined to the evidences of cyto- 

 plasmic movement during maturation and fertilization, leads me 

 to believe that definite movements of cell substance exist in the 



