30 
Proceedings of the Royal Society 
to suppose that these creatures can extemporise chords of contrac- 
tile tissue at will, and it explains in no way the subsequent 
retraction of the process. 
Within the last ten years, histologists, working at the ultimate 
structure of the cell, have brought to light facts which may bear 
upon this point, — facts in morphology the functional significance of 
which is not yet clearly known. 
Flemming, Strassburger, Klein, and others, have shown that 
“protoplasm” consists of two parts, — (1) a network or stroma, and 
(2) an inters tromal matter filling up the meshes of the stroma. All 
cells which have as yet been examined show these two parts both 
in the mass of the cell and in the nucleus. This stroma is an 
anatomical whole, although no doubt subject to slow changes 
during growth and division, as is the cell itself. In various cell- 
units the arrangement differs somewhat, but these general points 
may be alluded to. 
The stroma is a closed meshwork (not a stellate arrangement 
of particles), the tissue of which it is composed joining and 
anastomosing often, and at short intervals. The stroma is in 
connection with the nuclear wall, and with that of the cell if it 
be present. 
Now, in many cells this network has a distinct mechanical 
function. In the ciliated cell, as Klein believes, the stroma is the 
mechanism productive of the movements of the cilia. In in- 
voluntary non-striped muscular fibres the fibrils are homologues 
of the stroma, although they do not anastomose, being arranged in 
parallel series. The same holds good for the voluntary striped 
fibre, where the fibrillae representing the stroma (the cement is the 
homologue of the interstromal substance) perform the important 
function characteristic of the tissue — namely, contraction. It is 
seen then that in many cells the stroma lues a mechanical action 
possessing the power of contractility, which, however, is not the case 
with the interstromal matter. 
In those corpuscles which exhibit amoeboid movements , may not 
these be due to some contractions of the stroma which they , in com- 
mon with other cells , possess ? 
I may mention here that movements of the stroma of the white 
