158 THE CELL 



drops, when a solution of iodine in iodide of potassium is added 

 to them, acquire a mahogany -brown coloration, by means of which 

 they can be easily seen. 



Mucigenous substances often fill up the interior 

 of the cells, by which they are secreted (Fig. 

 64) in such quantities that the cells swell up 

 into vesicles, or assume the form of goblets. 

 The greater part of the protoplasm is collected 

 at the base of the cell, where the nucleus also is 

 situated, whilst the remainder surrounds the 

 mucigenous substance with a thin envelope, and 

 extends into it a few threads which unite together 

 to form a net. The mucigenous substances can 

 be clearly distinguished from protoplasm when 

 the cell is stained with one of several aniline 

 dyes. 



The internal plasmic products very frequently 

 acquire greater solidity in egg-cells, which are 

 loaded in the most various ways with reserve materials. These 

 are grouped according to their form as yolk-globules (Fig. 65), 

 yolk granules, and yolk lamellae, and from a chemical point of 

 view chiefly consist of a mixture of albuminates and fats. The 

 more numerous, small, and closely packed these yolk-elements 

 are, the more the plasmic body assumes a foamy or net-like ap- 

 pearance. 



FIG. 64.-Goble t - 

 cell from the blad- 

 der epithelium of 

 Squat ina vulgar!*, 

 hardened in Mfil- 

 ler'd fluid. (After 

 L.ist.PlateL.Fig.O.) 



Frs. G5.- Yolk elements out of a Hen's egg (after Balfour) : A yellow yolk spheres; 

 ]{ white yolk spheres. 



Many plasmic products are crystalline in character, such as the 

 guanin crystals, to which the glistening silvery appearance in the 

 skin and peritoneum of fishes is due, or as the pigment granules in 

 the pigment cells. 



Pla.smic products, similar to those in animal cells, occur also in 

 plant cells ; however, in this case they are generally present in a 

 few special organs, which are utilised either for the storing up of 

 reserve material, or, as with seeds, for purposes of reproduction. 



