JULY 14, 1899. ] 
structural elements of the cell may be 
termed living in a still more restricted 
sense. In its fullest meaning, however, 
the word ‘living’ implies the existence of a 
group of cooperating factors more complex 
than those manifested by any one substance 
or structural element in the cell, and Iam, 
therefore, thoroughly in accord with those 
who have insisted that life in its full sense 
is the property of the cell-system as a whole 
rather than of any one of its separate ele- 
ments. Nevertheless, we are perhaps justi- 
in maintaining that the continuous sub- 
stance is the most constant and active 
element, and that which forms the funda- 
mental basis of the system, transforming 
itself into granules, drops, fibrille or net- 
works in accordance with varying physio- 
logical needs.* 
Whether any or all of these elements are 
‘living’ or ‘lifeless ’ depends largely on the 
sense in which these words are used ; and 
itis well, therefore, to follow the example 
of Sachs, in substituting for these words, as 
applied to special structural elements of the 
cell, the terms ‘ active’ and ‘ passive,’ which 
properly admit of degrees of comparison. 
The distinction between ‘ protoplasmic’ 
(active) and ‘metaplasmic’ or ‘ paraplas- 
mic’ (passive) elements, though a real and 
necessary one, thus becomes, after all, one 
of degree only. 
We are thus brought to consider another 
point of some interest suggested by the 
comparative study of the facts described 
above. Butschli states that in the true or 
finer alveolar structure, characteristic of 
protoplasm in general, the alveoli do not 
measure more than 2.0 microns, and as a 
rule are considerably smaller. This, he in- 
* Tt is hardly necessary to state that this view is not 
original, except in so far as it has been directly sug- 
gested by the observations described above ; for it has 
been more orless definitely maintainedby many others, 
and I am only expressing what seems to be a grow- 
ing opinion among workers in this field. 
SCIENCE. 
43 
sists, is not to be confounded with a 
‘coarser vacuolization,’ characterized by 
larger drops or spheres, which may sec- 
ondarily arise in the finer structure. Again, 
Reinke and Waldeyer, in asomewhat simi- 
lar manner, characterize as ‘pseudo-alveolar’ 
a structure arising secondarily through the 
deposit of passive metaplasmic products of 
metabolism, such as yolk-spheres, fat-drops 
and the like, in the living protoplasmic 
basis. Both distinctions break down, I 
think, in the light of the foregoing facts. 
In most of the forms considered—Arbacia, 
Toxopneustes, Echinarachnius, Asterias — the 
alveolar spheres are considerably less than 
2.0 microns (1.0 to 1.7), and the structure 
is, therefore, a true alveolar one in Butschli’s 
sense; indeed, Butschli himself describes 
and figures the protoplasm of the Sphere- 
chinus egg as an example of that structure. 
In Ophiura, however, the spheres measure 
up to 3.0 to 4.0 microns, and are undoubt- 
edly ‘ yoke-spheres’ in the usual sense. It 
is, however, quite certain, from the ovarian 
development of these eggs, that they differ 
from the others only in degree, and that 
Butschli’s criterion of size gives no satisfac- 
tory ground for any real distinction. The 
alternative is to regard all the forms as 
pseudo-alveolar, irrespective of the size of 
the alveolar spheres, which are in all cases 
to be regarded as metaplasmic bodies ; and 
this is the view which Reinke specifically 
apples to Spherechinus. Butif this view 
be adopted we seek in vain for any ground 
of distinction between such a fine ‘ pseudo- 
alveolar’ structure as that of Arbacia and 
the ‘true’ alveolar structure of tissue cells, 
and are forced to the conclusion that in the 
latter case also the alveolar substance con- 
sists of passive or metaplasmic material 
—a view which has, in fact, been adopted by 
some writers. For my part, I am con- 
vinced that the entire distinction is without 
adequate basis, and that no definite bound- 
ary-line can be drawn between even the 
