GENERAL MORPHOLOGY OF THE CELL 



protoplasm which forms its living basis is a viscid, translucent, 

 granular substance, often forming a network or sponge-like structure 

 extending through the cell-body and showing various structural 

 modifications in different regions and under different physiological 

 states of the cell. Besides the living protoplasm the cell almost 

 invariably contains various lifeless bodies suspended in the meshes 

 of the network ; examples of these are food-granules, pigment-bodies, 

 drops of oil or water, and excretory matters. These bodies play a 

 purely passive part in the activities of the cell, being either reserve 

 food-matters destined to be absorbed and built up into the living 

 substance, or by-products formed from the protoplasm as waste 

 matters, or in order to play some role subsidiary to the actions of 

 the protoplasm itself. The lifeless inclusions in the protoplasm have 

 been collectively designated as metaplasm (Hanstein) in contradis- 

 tinction to the living protoplasm ; but 

 this convenient term is not in general 

 use. Among the lifeless products of 

 the protoplasm must be reckoned 

 also the cell-wall or membrane by 

 which the cell-body may be sur- 

 rounded ; but it must be remembered 

 that the cell-wall in many cases arises 

 by a direct transformation of the 

 protoplasmic substance, and that it 

 often retains the power of growth by 

 intussusception like living matter. 



In all save a few of the lowest and 

 simplest forms, perhaps even in them, 

 the protoplasmic substance is differ- 

 entiated into two very distinct parts, 

 viz., the cell-body, forming the princi- 

 pal mass of the cell, and a smaller 

 body, the nucleus, which lies in its 

 interior (Fig. 5). Both structurally 

 and chemically these two parts show 

 differences of so marked and constant 

 a character that they must be re- 

 garded as the most important of all 

 protoplasmic differentiations. The 

 nuclear substance is therefore often designated as nucleoplasm or 

 karyoplasm ; that, of the cell-body as cytoplasm (Strasburger). Some 

 of the foremost authorities, however, among them Oscar Hertwig, re- 

 ject this terminology and use the word "protoplasm" in its historic 

 sense, applying it solely to the cytoplasm or substance of the cell-body. 



a 



Fig. 6. A resting cell (.spermatogo- 

 niitm} from the testis of the salamander, 

 showing the typical parts. Above, the large 

 nucleus, with scattered masses of chro- 

 matin, linin-network and membrane. 

 Around it, the cytoplasmic thread-work. 

 Below, the attraction-sphere (a) and cen- 

 trosome (c). [After RAWITZ.] 



