1 



CELL DIVISION IN EGGS OF CREPIDULA. 523 



current. Among the many thousands of eggs so treated very few show any 

 trace of modification of the structure or orientation of the amphiaster. Where 

 the current is strong enough to produce any modification in the structure or 

 orientation of the mitotic figure it is usually strong enough to dislocate yolk, 

 cytoplasm and resting nuclei, as well as entire amphiasters, and to kill the eggs. 

 In such gross changes entire spindles, centrosomes as well as chromosome*, are 

 carried toward one pole, which judging by the work of Lillie, Pentimalii and 

 McClendon is the anode. In these experiments there is no indication whatever thai 

 the poles of the spindle bear electric charges differing in sign from the chromosomes 

 nor that the spindle fibres or astral radiations represent lines or chain* of force 

 between differently charged poles. If the forces which are at work in the iimphiaster 

 are electric, this could scarcely be the case, and it seems probable the fore that 

 the so-called " mitokinetic ' ' force is not electric. 



On the other hand I find evidence that the spindle fibres are composed of 

 relatively tough material and that they may be bent, distorted or displaced by 

 centrifugal force from their normal positions without losing their identity. In 

 this regard my results differ from those of F. R. Lillie (1909) and agree wit 

 those of Morgan (1910). Furthermore I find that the chromatic sap of the 

 nucleus forms the interfilar substance of the spindle and escapes, when the 

 nuclear membrane dissolves opposite the centrosomes, into the areas around the 

 centrosomes, and that it radiates from these areas and from the entire spindle 

 into the cell body by a process which resembles protoplasmic flowing in amoeboid 

 cells. By treatment with various chemical reagents, as well as with electricity 

 or increased temperature this flowing may be stopped and the processes or 

 radiations withdrawn into the central mass of archiplasm (hyaloplasm and chro- 

 matic sap) . The astral radiations are therefore expressions of diffusion streams, 

 rather than of electric lines of force. Of course it is probable that there is a 

 difference of potential between the electric charges carried by the particles of 

 this chromatic sap, and the colloidal particles of the cell body, but it also seems 

 probable that the spindle figure and its radiations are due in the first instance 

 to the escape and diffusion of nuclear substances into the cell body, rather t han 



to the electric potentials of these substances. 



Whenever two or more astral systems are present the chromosomes at first 

 take up positions between them. Between two such centers the chromosomes 

 form a rectilinear equatorial plate, and when many centers are present the area 

 around each is bounded by a line of chromosomes, the whole forming a compli- 

 cated pattern of hexagonal or polygonal areas, each inclosing a centrosome and 

 bounded by chromosomes. Such a condition would be produced if centrosomes 

 and chromosomes carried like charges, as Lillie maintains. This condition is fol- 

 lowed quickly by a stage in which the daughter chromosomes separate from one 

 another, and, as daughter plates, approach the centrosomes. This movement 

 might, conceivably, be due to the daughter chromosomes carrying like charges 

 and consequently repelling each other; however there is, on this hypothesis, no 



