UTRICULAR STRUCTURES. 173 



The nucleoli occur inside the nuclear utricles and the 

 spermatic utricles.* Nothing is known of their mode 

 of origin. In animal nucleoli a process of division has 

 been observed, f 



The shape of the nucleoli is globular ; at the moment 

 when they originate by division, hemispherical. If they 

 lie upon the membrane of the nuclear utricle, they are 

 sometimes flattened on that side. The contents of the 

 nucleoli are originally homogeneous and mucilaginous, 

 and usually exhibit greater density than those of the 

 nuclear or spermatic utricles ; in rare cases they are less 

 dense, causing the nucleolus to appear like a hollow 

 space. The homogeneous contents of the nucleolus sub- 

 sequently become frothy and granular ; or they remain 

 homogeneous and exhibit one or more cavities. 



4. Mucilage- (Protoplasm-} utricles (Schleimblaschen).J 



These structures have hitherto been either overlooked, 

 or taken for large mucilaginous granules or for globules of 

 agglomerated mucilage. They may be seen beautifully, 

 and in great abundance, in the Characese, where, together 

 with amorphous masses of mucilage, they are the chief 

 bodies seen to rotate. I have also seen them in the cells 

 of many Algse, of the leaves of Mosses and Hepaticee, in 

 the Perns and the Phanerogamia. They do not present 

 themselves constantly, and mostly but sparingly, 1 6 

 in a cell. They are more certain to be found in large 

 cells than in small. 



The mucilage-utricles are distinguished from the mu- 

 cilaginous granules by their much more considerable size, 

 by possessing a perfectly spherical shape and a smooth sur- 

 face, and by refracting light less. That they are utricles, 



* Nageli on Cells, &c. ; Ray Translation, 1845, pi. vii, fig. 11 a. Nageli 

 on Moving Filaments, &c., loc. cit. pi. iv, fig. 16, a, b, c. 



j- KdlliSer, Entwick. der Cephalopoden, pi. vi, fig. 68. 



5 I refer the reader to the observation made in the preceding essay 

 (p. 124) on the term " mucilage" (schleim). 



