174 . UTRICULAR STRUCTURES. 



and not homogeneous granules, follows from this : 1st, 

 that when large enough, a membrane may be detected 

 on them which is not coloured by iodine, while the con- 

 tents become brown (pi. II, fig. 18) ; and 2d, that the 

 mucilaginous contents may become frothy and hollow. 

 The membrane becomes especially manifest, when the 

 contracting contents separate in places from the mem- 

 brane, in utricles which come in contact with water or 

 tincture of iodine (fig. 18, b, c). 



Little can be observed of the origin of the mucilage- 

 utricles. They first appear as very minute globules of 

 mucilage. It is possible that a small quantity of muci- 

 lage becomes agglomerated, individualized, and acquires 

 a membranous covering. I have not observed a propaga- 

 tion of the mucilage-utricles. 



The shape of the mucilage-utricles is spherical from 

 the beginning, and it always remains so. The growth 

 serves merely to expand the utricles uniformly. 



The contents are originally homogeneous. They remain 

 in this condition, or one or more hollow spaces appear in 

 them. 



The membrane is delicate, and seldom attains any con- 

 siderable thickness. In Chara and Nitella only have I 

 yet seen the mucilage-utricles with tougher membranes. 

 The membrane is also thin here originally, and either in- 

 visible or only indistinct. By the application of iodine 

 we may mostly succeed in seeing it more clearly. It then 

 appears distinctly bordered by two lines (Fig. 18, a). At 

 a later period minute points (V) appear on the outer 

 surface, which with the increase of size show themselves 

 to be little spines (c, e). In old utricles the spines dis- 

 appear, and the outer surface of the membrane is irregular 

 and uneven (d). During this the membrane has been 

 constantly increasing in thickness. 



Looking for an analogy for the spines just described, 

 one might think of the cilia of the germ-cells of Vauclieria, 

 and notice that the mucilage-utricles of the Characere 

 likewise move (rotate), while the mucilage-utricles of other 



