REJUVENESCENCE IN NATURE. 171 



Hydrodictyon, I have most clearly observed a composition 

 of the mucilaginous layer of three distinct lamellae. When 

 the cells of the full-grown Water-net are treated with 

 dilute hydrochloric acid, the entire contents are ordinarily 

 contracted from the cell-membrane as a closed utricle or 

 tube, smooth on the surface, and no laminar separation 

 can be detected in it. Sometimes, however, and as it 

 appeared to me, in diseased cells, previously near their 

 dissolution, there occurred, as in (Edogonium, a separation 

 into an outer paler, and an inner, dark-green utricle, the 

 former exhibiting a smooth, the latter a rough surface, 

 and remaining connected here and there with the outer 

 utricle by thick mucilaginous threads or trabecula, which 

 originated through the inner, more strongly contracting 

 utricle, drawing out the mucilaginous substance of the 

 outer in the form of filaments, at these points, where it 

 does not become completely detached from it. This 

 phenomenon would not speak in favour of a membranous 

 structure and consistence of the outer utricle ; but further 

 investigation shows that this outer utricle is not simple, 

 but formed of two distinctly different layers, an extremely 

 delicate pellicle, accurately defined inside and out, and a 

 less sharply defined, somewhat thicker layer of mucilage, 

 which two layers separate from one another at various 

 places, so that they may be very clearly distinguished. 

 The entire contents of the cell of Hydrodidyon exhibit, 

 proceeding from without inwards, the following sections: 

 1 . The primordial membrane. It is of scarcely mea- 

 surable thickness, colourless, opakish, and very finely 

 and uniformly punctated, which depends on its being 

 composed of closely conjoined, extremely minute globules, 

 which, according to my estimate, can be at most between 

 355otli and g^oth of a rnillim. in diameter. This extremely 

 delicate structure has a totally different character from 

 the inmost layers of the cell-membrane, for it is dimin- 

 ished in diameter, and retracted from the cell-membrane 

 by the action of acids, while the inmost layers of the 

 cellulose remain connected with entire cell-membrane, 



