PROTOPLASM AND THE OELL. 5 



Several opinions have been given in regard to the structure of the cyto- 

 plasm, in addition to that here presented, according to which it may be 

 compared to a sponge the meshes of whose network are occupied by the 

 cytolymph. According to another view it is composed of a number of 

 fibrils of varying lengths imbedded in a matrix, the fibrils corresponding to 

 the reticulum of the reticular theory and the matrix to the cytolymph. 

 According to still another theory which rests on the appearance produced 

 in the cytoplasm by a special method of treatment, there is present a color- 

 less matrix in which are imbedded numerous exceedingly small granules 

 sometimes scattered and sometimes united together into chains. Indeed 

 the upholder of this granular theory has carried his view to the extent of 

 regarding the granules as structural units of which the cell is composed, 

 its structure being comparable to that of a zoogloea of micrococci. It 

 seems probable, however, that the granules are to a large extent secondary 

 products of the activities of the cytoplasm and have therefore but a sub- 

 ordinate value in its composition. The reticular theory seems to stand 

 more nearly in harmony with the majority of observations, though it 

 must be admitted that some observers do not seem to have perceived the 

 true reticulum, confining their attention to the coarser network produced 

 in some cases by extensive vacuolization of the cell. 



An imitation of the cytoplasm has been recently obtained by the mix- 

 ture of thickened oliye-oil with a solution of potassium carbonate or of 

 chloride of sodium, the watery solution taking the form of polyhedral 

 globules each surrounded by a thin layer of oil which from its higher 

 refractive index gives the appearance of the plastin reticulum surrounding 

 the cytolymph. Solid particles finely divided and mixed with the oil tend 

 to collect at the points where the oil-films of three of the globules come 

 together, and resemble the microsomes, while it is further noticeable that 

 under certain conditions the superficial globules of the emulsion take on a 

 columnar form and maybe compared with the ectoplasm of the cell. It 

 is possible that the cytoplasm may have this structure, in which case the 

 reticular theory would require to be modified, since there would no longer 

 be a spongy structure, but rather an emulsion in which the cytolymph is 

 divided into a number of globules each surrounded by a thin layer of 

 plastin. At present, however, the reticular theory seems to correspond 

 most accurately with the actual appearances, and therefore may be pro- 

 visionally accepted. 



The caryoplasm or nucleus, as already stated, lies usually 

 about the middle of the cytoplasm and to a certain extent re- 

 sembles it, though it presents certain peculiar features. It 

 is usually round or oval, though occasionally it may assume 

 elongated, horseshoe-shaped, moniliform, or even branching 

 forms, and is as a rule clearly marked oif from the cytoplasm by 

 a membrane (Fig. 1, mm), which, however, at certain periods of 



