104 TlMEHRI. 
surrounded , with a thin coat or cuticular layer quite 
different from cellulose. 
The lowest forms of plants and animals, and necessarily 
those of doubtful position, consist simply of a single cell, 
which may be of very diverse form caused either by arm- 
like or hair-like extensions of its protoplasm, or by the 
secretion of a test or shell, generally of calcareous or sili- 
ceous matter. As we advance higher in the scale of organi- 
sation, we find plants and animals composed of aggrega- 
tions of cells, the unicellular becoming the multicellular, 
individual cells being variously modified to form the 
different vessels, fibres and tissues of the higher organ- 
isms, in which, as for instance among animals, we meet 
with nerve-cells, muscle-cells, bone-cells, reproductive- 
cells, etc., each modified to perform different functions. 
In all cases, the complex organisation of the higher 
form has been derived from a single cell, commonly 
known as the egg-cell — in other words, all these organ- 
isms start life as a single cell, in which temporary stage 
they are comparable to the permanent stage of the 
lower forms or Animalcules. In all cases, the reproduc- 
tive cells are those which are least modified from their 
original charafter, and are those alone which ever take 
on the temporary, primitive stage of an unicellular 
organism. 
From what has been said, it will be seen that the 
Animalcules are almost invariably unicellular beings ; 
and in the fact that all the complicated apparatus of the 
higher organisms has been developed from cells com- 
parable to the simple cells of the Animalcules, will be 
found an explanation of the wonderful condition met 
with in the lower types, in which the one cell performs, 
