CHROMATIN — DEVELOPMENT AND HEREDITY 235 



cleavage plane. The chromosomes are arranged in the equatorial 

 plate. In the cytoplasm, toward the first cleavage plane, occur 

 several chromosomes which are attached to astral fibers extend- 

 ing from one of the poles of the spindle. These might be inter- 

 preted as chromosomes which did not reach the nucleus during 

 the first cleavage, but which have persisted in the cytoplasm. 

 Frequent observation of the same phenomenon in other hybrid 

 material has led me to think that this elimination took place 

 during the prophase of this mitosis. In a normal prophase the 

 elongating astral fibers push the chromosomes before them and 

 when the asters have attained their normal distance from each 

 other the equatorial plate is established. The abnormality 

 shown in figure 25 consists in the extra growth of some of the 

 astral fibers of one or both asters toward the previous cleavage 

 plane. These fibers are always attached to chromatin and, in 

 consequence, they stain deeply, as do the spindle fibers. The 

 depth of the stain depends upon the number of fibers and this, 

 in turn, upon the amount of chromatin extruded. In the cross 

 between Stenotomus chrysops and Ctenolabrus adspersus to be 

 described later, I have found the same process of elimination 

 occurring. In a few instances the amount of chromatin expelled 

 is very slight and only one or two astral fibers are involved. 

 These fibers, although staining more definitely than the astral 

 fibers to which no chromatin is attached, do not form as striking 

 a picture as when the disturbance is greater. The unusual 

 convexity of the spindle in the direction of the astral outgrowth 

 suggests a lowering of the surface tension in the region of the first 

 cleavage plane. 



Figures 20 and 21 are the two cells of one egg. Figures 24 

 and 25 show the condition found in another egg of the same lot. 

 In the egg from which drawings 22 and 23 were made no trace 

 of such an occurrence is to be found. 



Without more evidence these facts cannot be made the basis 

 of a conclusive interpretation, but I think they indicate strongly 

 that an elimination of chromosomes does occur in some of the 

 individuals of this cross. It is also evident that the abnormali- 

 ties in division, both lagging and elimination, are not regular in 

 their occurrence. 



