338 T. H. BAST 



PLATE 1 



EXPLANATION OF FIGURES 



All of these drawings are camcra-lucida drawings of cells from the entire pari- 

 etal bones of young rats, except figures 3, 4, and 5, which were taken from the 

 ethmoid bone of a dog. These bones were fixed in 95 per cent alcohol and stained 

 in gentian violet. The original magnification as indicated for each figure was 

 reduced | in reproduction. 



1 Normal bone cell from fifteen day-old rat. The nucleus is oval in shape. 

 X 1200. 



2 Cell in early stage of division. Nucleus dumbbell shaped. Centrosomes at 

 opposite poles of nucleus. Two large masses of protoplasm almost separated from 

 main cell. X 1200. 



3 Cell from ethmoid bone of dog. A little later stage of nuclear division than 

 figure 2. Cytoplasm is not constricted. X 1450. 



4 Cell from ethmoid bone of dog. Nucleus completely divided. Cytoplasm 

 constricted. Centrosomes are faintly seen, but the centrioles are not visible. 

 X1450. 



5 Cell from the ethmoid bone of a dog. Early stage in the horseshoe type of 

 amitosis. The centrosomes are placed at the center of the horseshoe-shaped 

 nucleus. X1450. 



6 The horseshoe-shaped nucleus has just divided. Centrosomes at the center. 

 X 1600. 



7 A later stage in the division of a horseshoe-shaped nucleus. The two 

 daughter nuclei are kidney shaped and only slightly separated. The centrosomes 

 are four in number and still centrally placed. X1600. 



8 Late stage in the horseshoe type of amitosis. The cytoplasm is deeply 

 constricted. The irregular shaped nuclei are due to improper fixation. X1450. 



9 These three nuclei are the product of the division of a horseshoe-shaped 

 nucleus. Centrosomes centrally placed. X1600. 



10 Three cells derived from a cell with a horseshoe-shaped nucleus. The 

 nuclei of these cells are already in the early stage of division. X1450. 



11 Pentanucleated cell with the nuclei still arranged in the shape of a horse- 

 shoe. Multicorpuscular centrosome within ring of nuclei. X1600. 



12 Four cells which are probably the product of a tetranucleated cell. Note 

 the large protoplasmic connections. X1600. 



