FORMATION OF POLAR SPINDLE IN I5UFO. 8$ 



place at this time. During this period the chromosomes are ex- 

 ceedingly varied in size and shape. If the chromosome is oblong, 

 it may have either its long or its short axis parallel with the lon- 

 gitudinal axis of the spindle ; if the chromosome is pyramidal in 

 shape, either the base or the apex of the pyramid may rest on 

 the spindle fibers. I regard all of the changes in the shape of 

 the chromosomes up to the stage of Fig. 7 as due solely to a 

 rearrangement of the chromatin material preparatory to the later 

 divisions. The first indication of any division of the chromo- 

 somes is the longitudinal splitting of the lateral wings which in 

 some few cases can be found before the disappearance of the polar 

 arms (Fig. 7). The apparent separation of the lateral wings at 

 X, Fig. 1 1, I consider to be due to the fact that the angle of the 

 V-shaped chromosome was cut off in sectioning. It very fre- 

 quently happens that portions of one or of several chromosomes 

 on a spindle are removed in this way. Sometimes, as in Fig. 4, 

 the median knob of a chromosome is lacking ; sometimes, the 

 lateral wings have been removed (Figs. 6, 7). In rare instances 

 the cut off portion of the chromosome will be found in the next 

 section of the egg ; but as the chromosomes are quite small a 

 careful examination of the following sections often fails to dis- 

 close the missing part. 



As found to be the case in many eggs besides that of Bufo, 

 for example in Cerebratulns (Coe), PolycJiccrus candatns (Gardiner), 

 Thalasscma and ZirpJicea (Griffin), and Triton (Carnoy and Le- 

 brun), all the chromatin of the germinal vesicle does not go to 

 form the chromosomes of the first polar spindle, some of it is 

 thrown out into the cytoplasm where it degenerates and sooner 

 or later completely disappears. Even in the segmentation stages 

 of the egg of Asian's, Boveri (i) found that some of the chrom- 

 atin is thrown out of the nucleus and absorbed by the cytoplasm. 

 In all these cases there is obviously a mass reduction of the 

 chromatin in preparation for the succeeding division of the cell. 

 It may be, as suggested by Gardiner, that " there are two kinds 

 of chromatin stuff, the one insoluble and bearing the heredity 

 which is to be transmitted to the daughter cells, and the other food 

 for the cytoplasm." This theory would explain the facts as we 

 now know them, but it cannot be proved until some stain can be 

 found to differentiate the two sorts from each other. 



