1853.] OF THE ROYAL INSTITUTION. 301 
mordial utricle in woody cells in general, — in confirmation of the 
same views. 
Now, these metamorphoses of the periplastic substance are two- 
fold: 1. Chemical, 2. Morphological. 
The Chemical changes may consist in the conversion of the 
cellulose into xylogen, &c. &c. or in the deposit of salts, silica, 
&c. in the periplastic substance. Again, the periplastic substance 
around each endoplast may remain of one chemical composition, 
or it may be different in the outer part (so-called intercellular 
substance) from what it is in the inner (so-called cell-wall). 
As to Morphological changes in the periplastic substance, they 
consist either in the development of cavities in its substance — 
vacuolation (development of so-called intercellular passages) or in 
fibrillation (spiral fibres, &c.). 
It is precisely the same in the Animal. 
The Endoplast may here become differentiated into a nucleus 
and a primordial utricle (as sometimes in Cartilage) or more usually 
it does not,— one or two small solid particles merely arising or 
existing from the first, as the so-called ‘‘ nucleoli ;’’— it persists for 
a longer or shorter time; it divides and subdivides, but it never 
(except perhaps in the case of the spermatozoa and the thread-cells 
of Medusz, &c.) becomes metamorphosed into any tissue. 
The periplastic substance, on the other hand, undergoes quite 
independent modifications. By chemical change or deposit it ac- 
quires Horn, Collagen, Chondrin, Syntonin, Fats, Calcareous Salts, 
according as it becomes Epithelium, Connective Tissue, Cartilage, 
Muscle, Nerve or Bone, and in some cases the chemical change 
in the immediate neighbourhood of the endoplast is different from 
that which has taken place exteriorly,— so that the one portion 
becomes separable from the other by chemical or mechanical means ; 
— whence, for instance, has arisen the assumption of distinct walls 
for the bone-lacune and cartilage-cavities; of cell-contents and of 
intercellular substance as distinct histological elements. 
The Morphological changes in the periplastic substance of the 
animal, again, are of the same nature as in the plant : — Vacuola- 
tion and Fibrillation (by which latter term is understood, not only 
the actual breaking up of a tissue in definite lines, but the tendency 
to do so) —Vacuolation of the periplastic substance is seen to 
its greatest extent in the ‘‘ Areolar”’ connective tissue ; — Fibril- 
lation in tendons, fibro-cartilages and muscles. 
In both Plants and Animals, then, there is one histological ele- 
ment, the Endoplast, which does nothing but grow and vegetatively 
repeat itself; the other element, the periplastic substance, being the 
subject of all the chemical and morphological metamorphoses, in 
consequence of which specific Tissues arise. The differences be- 
tween the two kingdoms are, mainly, 1. That in the Plant the 
Endoplast grows, and, as the primordial utricle, attains a large com- 
parative size;— while in the Animal the Endoplast remains small, 
