38 SCIENCE. 
briefly, the alveoli, though, strictly speaking, 
the latter term should designate the cavi- 
ties which the spheres fill. The clear basis 
in which they lie, and which forms the inter- 
alveolar walls, may, with Mrs. Andrews, be 
called the continwous substance. Scattered 
about in the walls are numerous granules, 
or microsomes, far smaller than the alveoli, 
which often give the appearance of an irreg- 
ular network. If now we compare these 
appearances of the living protoplasm with 
those seen in the sections mounted in bal- 
sam we find at first sight very considerable 
differences. More critical study shows, 
however, that the differences are almost 
wholly due to the effect of differential 
staining and to the difference of refractive 
index in the mounting media in the two 
eases. The alveoli of the living protoplasm 
form the spaces of themeshwork. Thelat- 
ter consists of the continuous substance with 
the granules suspended in it. In the sec- 
tion what especially strikes the eye is the 
meshwork ; for the alveolar spheres do not 
stain, and their contours become indistinct 
in the highly refracting balsam, while the 
continuous substance stains slightly, and 
the granules intensely, thus giving the ap- 
pearance of a conspicuous granular mesh- 
work. We thus arrive at a definite answer 
to two of the questions propounded above, 
namely: (1) the meshwork shown in 
sections is not a network, but the expres- 
sion of an alveolar or emulsion-structure, 
and (2) proper fixation does not produce a 
mass of coagulation-artefacts, but preserves 
the visible structure very nearly as it ex- 
ists in life. 
The above conclusions are based mainly 
on the study of star-fish eggs, but are con- 
firmed by the facts observed in other forms. 
In Arbacia the emulsion is considerably 
finer, the alveoli measuring on an average 
no more than 1.0 micron, while the finer 
granules are relatively less numerous. The 
pigment-granules characteristic of this form 
IN. S. Vou. X. No. 237. 
appear to be nothing other than modified 
alveolar spheres. In Toxopneustes the al- 
veoli measure approximately from 1.0 to 1.3 
microns, while the granules are more nu- 
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Fic. 2. (a) Protoplasm from a living ophiuran egg 
(Ophiura), slightly compressed, so as to spread the 
yolk-spheres somewhat apart ; ) the same as seen in a 
section (sublimate-acetic, iron-hematoxylin ; 1,200 
diameters). 
merous than in Asterias. In Eehinarachnius 
the alveoli are less uniform in size than in 
Asterias, the largest measuring up to about 
1.7 microns, while the granules are less 
numerous. The egg of Ophiura, finally, 
has an extremely coarse structure, the alveo- 
lar spheres measuring on an average 3.0 to 
4.0 microns, while the granules, or micro- 
somes, are also very large and, in the super- 
ficial layers of the protoplasm, even more 
numerous than in Toxopneustes. The proto- 
plasm of Ophiwra (Fig. 2) is highly favor- 
able for study, not only on account of the 
great size of its elements, but also by reason 
of the remarkable fact that these elements 
are colored in life, the alveolar spheres be- 
ing in most individuals distinctly of an 
olivaceous or pinkish-brown color, while 
