British Association. 
[September, 
630 
the Protamceba. Towards its centre a small globular mass of 
firmer matter has become differentiated from the remainder, 
forming a nucleus, while the protoplasm constituting the extreme 
outer boundary differs slightly from the rest, being more trans- 
parent, destitute of granules, and apparently somewhat firmer 
than the interior. We may also notice that at one spot a clear 
spherical space has made its appearance. On watching we see 
it suddenly contract and vanish, and after a few seconds it 
dilates, comes into view, and again disappears, — all this in regu- 
lar rhthymic sequence. This pulsating cavity is the “ contractile 
vacuole.” In the Amceba we have the essential characters of a 
cell, the morphological unit of organisation and the physiological 
source of specialised function. The term “ cell ” is, however, 
somewhat misleading; it denotes merely a definite mass of 
protoplasm containing a nucleus, which may or may not assume 
the form of a vesicle. To the non-nucleated forms of life, such 
as Protamceba, Haeckel assigns, in distinction, the name Cytode. 
Many aquatic beings beside the Amceba never pass beyond the 
condition of a simple cell, in which reside the whole of the pro- 
perties which manifest themselves in the vital phenomena of the 
organism. As we pass from these lowest forms to higher we 
find cell added to cell, until many millions of such units become 
associated in a single organism, where each cell or group of 
cells has its special work, while all combine for the welfare and 
unity of the whole. Still even in man the component cells are 
far from losing their individuality. The colourless blood-cor- 
puscules retain most of the characters of the Amoeba. 
The animal egg, which in its young state forms an element in 
the structure of the parent organism, is a true cell, consisting of 
a lump of protoplasm enclosing a nucleus, and having in the 
interior of this a nucleolus. Whilst still very young it has no 
constant form, and may, like an Amceba, wander about by the 
aid of its pseudopodial projections. The life of an organism is 
made up of the lives of its component cells, and here we find 
most distinctly expressed the great law of the physiological 
division of labour. In the lowest unicellular organisms the 
performance of all the processes which constitute its life must 
devolve on the protoplasm of this one cell ; but as we pass to 
more highly organised beings the work is distributed among a 
number of workers, — to wit, the cells which make up the com- 
plex organism. No cell, however great may be the differentia- 
tion of function in the organism, can dispense with its irritability, 
the one constant and essential property of every living cell. In 
very many instances the protoplasm becomes confined within 
resisting walls, composed in plants of cellulose, still losing none 
of its activity, as is manifest in the Characeae, in Valisneria spi- 
ralis , and even in higher plants. Even in these higher plants, 
further, truly naked protoplasm still occurs, as has recently been 
shown by Mr. F. Darwin in the teazel ( Dipsacus ) — a phenome- 
