146 bulletin: museum of comparative zoology. 



preparations stained in Kernschwartz and safrauiu. In Figure 44 the 

 middle nucleus has an irregular outline on the side toward the greater 

 cytoplasmic mass. Two small granules lie close to the nuclear mem- 

 brane, each one opposite a slight concavity of the nucleus. Each gran- 

 ule is surrounded by a clear space. From both granules radiations 

 extend into the cytoplasm, some of them going in straight lines nearly 

 to the cell periphery, others (those directly opposite the nucleus, in the 

 middle region of the cell) showing an arrangement like that described 

 in the nerve cells. The primary radiations from the centre meet gran- 

 ules from which go off secondary radiations, resulting in something 

 of a radiating network of fibres with granules at their intersections. 

 The radiations,- like those of the nerve cell, appear either as hyaline 

 fibrils, or as rows of granules. The presence of the two central granules 

 in Figure 44 suggests preparation for mitosis. 



In Figure 45 the larger nucleus has a sharp invagination at its deeper 

 end. Opposite the invagination is a granule with a complex radiating 

 system about it. Primary, secondary, and tertiary radiations may be 

 detected. 



VII. Mitosis in the Regenerating Epidermis. 



Figures 46-52 (Plate 7) represent stages in the mitosis of cells in 

 the regenerating epidermis of a single worm. Figure 46 shows a cell in 

 the prophase. The chromatin has assumed the form of nearly spherical 

 chromosomes. The nuclear membrane is still present, but indistinct or 

 absent at the regions where the spindle comes into relation with the 

 chromosomes. No distinct granules could be detected at the spindle 

 poles. Well defined polar radiations are present. The cytoplasm is 

 fairly dense throughout the cell, and there is a distinct cell membrane. 

 The deformation of adjoining cells shows that the cell has increased in 

 volume. This condition is followed by the total disappearance of the 

 nuclear membrane, and the chromosomes are assembled into an equa- 

 torial plate. Figure 47 shows the daughter chromosomes on their way 

 toward the poles. Indistinct interzonal filaments are present. The 

 centrosoraes are extremely minute, but definite granules. Numerous 

 polar radiations extend to the periphery throughout the entire cell. 



Figure 48 shows a cell seen from the surface of the epidermis, the 

 axis of the nucleus being perpendicular to that of the cell. The nuclear 

 figure is in the telophase with barrel-shaped interzonal region. The 

 centrosomcs could not be found. Figures 46-52 are, with the exception 

 of Figure 48, all from a limited region of epidermis at the ventral edge 



