132 
POPULAR SCIENCE REVIEW. 
A good idea may be formed of the appearance of the simpler 
kind of vegetable cell by an examination of Protococcus or 
Palmella , both of these organisms being exceedingly common 
and obtainable at almost any season of the year. In Palmella , 
as will be seen on reference to the annexed woodcut, fig. 1, the 
cells are surrounded by an externally investing gelatinous layer, 
a, of which no mention is made in the definition, owing to its 
being regarded as a mere occasional and supplementary appen- 
dage. This view, however, appears to me to be insufficiently estab- 
lished, inasmuch as there is reason to believe that it is present 
in the unicellular algae generally, though often in such an ex- 
tremely attenuated state as to be invisible even with the aid of 
the highest powers of the microscope ; and the evidence of its 
existence is in these cases derived altogether from analogy and 
Fig. 1. 
C 
The three figures a, b, and c, represent specimens of Palmella before division, 
after division into two, and these two, after subdivision into four distinct indi- 
vidual cells. The small letters indicate the same parts in each case — a, 
the external jelly-like matrix; b, the “ primordial utricle ” of Mold ; c, the 
cellulose wall ; and d, the coloured and granular endochrome. It will be seen 
that the gelatinous investiture does not participate in the division. 
observed phenomena in the organisms which are inexplicable on 
any other supposition than that some external investiture is 
present. But, apart from the question of its invariable presence, 
it becomes a matter of great importance to determine whether 
the gelatinous substance continues, so long as the parent struc- 
ture lives, to participate in its vitality, or whether it ought to 
be regarded as effete and dead.* It is so perfectly hyaline and 
amorphous that the microscope fails to reveal in it the slightest 
trace of structure. And yet amongst the Diatomacese it as- 
sumes such a variety of characters, and is in some instances 
endowed with such a marvellous degree of elastic and contrac- 
tile power, during the lifetime of the parent organism, but no 
longer , as to suggest the inference that it resists decay and dis- 
integration solely through some vital bond between it and the 
cell contents. 
* The case is probably met by regarding it, in accordance with Dr. Beale’s 
view, as “ formed material,” although not in the sense of its being devoid of a 
low degree of vitality. 
