170 UTRICULAR STRUCTURES. 



When the nucleus originates free, it is in its earliest 

 condition globular; when it originates with a fellow- 

 nucleus in a parent-nucleus, it is originally hemispherical, 

 but then, separating from its fellow, it rapidly assumes a 

 globular shape.* The nucleus retains its spherical shape 

 if central in its cell ; it only becomes ellipsoidal when 

 about to propagate ; but if the nucleus occupies a lateral 

 position in its cell, it becomes flattened on one side. Seen 

 in front, it then appears circular or ellipsoidal, while 

 laterally it seems more or less compressed. 



The growth of the nucleus is sometimes very slight ; 

 sometimes an expansion of from twice to ten times its 

 diameter takes place. 



The membrane of the nucleus never acquires any 

 considerable thickness, and never exhibits lamellation or 

 lignification as in cells. 



Young nuclei, as well when they have originated free 

 as by division, generally possess homogeneous, colourless 

 mucilaginous contents. These may be dense and opaque, 

 or almost transparent. Subsequently they become gra- 

 nular, and we may then distinguish a transparent fluid, 

 mucilage-granules, starch- granules, chlorophyll-granules, 

 and drops of oil. Sometimes the homogeneous and 

 granular mucilage becomes deposited in the form of a 

 layer on the inner surface of the membrane, so that the 

 rest of the cavity is filled merely with watery fluid. 

 Sometimes the nucleus contains amorphous colouring 

 matter, so that it appears homogeneously redf or green. J 

 Amorphous chlorophyll may also clothe the inner surface 

 of the membrane, merely in patches. For more minute 

 particulars, I refer to my earlier essay on this subject. || 



There are generally from one to three nucleoli in the 

 contents of the nucleus; sometimes their number rises 

 to five and six. These nucleoli appear to be rarely absent. 

 Probably they are always present, and merely invisible 



* Mgeli on Cell-Formation; Ray Trans., 1845, p. 184, pi. vii, fig. 20. 

 f Loc. cit, 1845, pi. vi, fig. 26. Loc. cit, pi. vi, figs. 36-40. 



Loc. cit. pi. vi, fig. 41. || Loc. cit. p. 219 et scq. 



