THE VITAL PROPERTIES OF THE CELL 



159 



Under such, circumstances the cells are filled with drops of oil 

 (oily seeds), with granules of various albuminous substances 

 (vitellin, gluten, aleuron), with crystalloids of proteinaceous sub- 

 stance, or with starch granules, about which more will be said 

 later. 



The above-mentioned internal plasmic products being only tem- 

 porarily accumulated during metabolism before being utilised, 

 vary considerably in composition, but there are others which 

 attain a higher degree of organisation, and which participate 

 permanently in the functions of the cell. To such belong the 

 internal skeletal structures of the protoplasm, the various sub- 

 stances in plant cells, described under the common name of 

 trophoplasts, the cnicloblasts of Ccelenterata, and, finally, the 

 sheaths of the muscle and nerve fibres, etc. 



Internal skeletons 

 are found in the bodies 

 of a large number of 

 Protozoa, but especi- 

 ally in great variety 

 and beauty in Radio- 

 larians. They consist 

 sometimes of regularly 

 arranged spicules, 

 sometimes of a fine, 

 open trellis- work, and 

 sometimes of a com- 

 bination of the two 

 kindsof structures (Fig. 

 (6). In some families 

 of Radiolarians they 

 are composed of an or- 

 ganic substance which 

 is soluble in acids and alkalies, but in most cases, on the contrary, 

 they consist of silicious material which is united to an organic 

 substratum, just as, in the bones of Vertebrates, the phosphates 

 are united with the ossein. In each species the skeleton has a 

 constant and characteristic structure, and follows certain fixed 

 laws during the process of its development (Richard Hertwig, 

 5, 40). 



Under the name trophoplasts, the highly organised differen- 

 tiated products of vegetable protoplasm are included ; these occur 



Fig. 66. Haliomma erinaceus (from R. Hertwi?, Zool., 

 Fig. 82) : a external, i internal trellis work ; ck central 

 capsule ; wk soft extra capsular body ; 7i internal vesicle 

 (nucleus). 



