THE CELL 



can 



'cy. 



it is composed has undergone further differentiation, as may be seen in 

 Figure i. 



The nucleus is clearly defined from the cytoplasm by a film of spe- 

 cialized karyoplasm which has generally been looked upon as having a 

 membranous texture and has, therefore, received the name nuclear mem- 

 brane. The nature of this membrane has not yet been satisfactorily 

 determined. The nuclear membrane incloses a transparent, refractive 

 fluid, the hyaloplasm. 



Supported by the hyaloplasm is a network of non-staining refractive 

 threads which form a scaffolding upon which other karyoplasmic struc- 

 tures are distrib- 

 uted. These 

 threads are com- 

 posed of the linin 

 of the nucleus. 



Tangled with- 

 in the linin 

 meshes are usu- 

 ally to be seen 

 from one to 

 many rather 

 large, rounded 

 bodies which 

 stain more read- 

 ily than the linin 

 and are relatively 

 dense and highly 

 refractive. These 



are the nucleoli FIG. 5. Dorsal nerve cell from cord of Pterophryne histrio. ca., blood 

 Or blasntOSOmCS capillaries containing blood corpuscles; ., nucleus of nerve cell; ca.n., 

 . nuclei of capillary wall ; cy., cyto'plasm. X 400. 



Their form va- 

 ries. In some instances they are rod-shaped, in others they become 

 angular lumps. Their texture is homogeneous. They frequently in- 

 close vacuoles (Fig. 5). 



The most essential parts of the karyoplasm are the deeply staining 

 granules which are supported upon the linin network. These are quite 

 probably the homologues of the deeply staining granules of pseud ocysts, 

 and they have suggested the name for the latter, they having been called 

 chromatin. The chromatin in a cell that is not dividing is distributed 

 through the nucleus in a number of particles of irregular shape, as in 

 Figure i. These chromatin grains are usually many and are clearly 

 defined ; but they may be either few and relatively large or so extremely 

 minute that they are individually invisible and give a cloud- like appear- 



