oj Edinburgh, Session 1883 - 84 . 287 
the explanation of such problems of cell structure and contractility 
as those briefly enumerated above. 
On this view, the granules of such a low vegetable organism as 
Torula (disregarding, of course, sap vacuoles and fat globules) are 
aggregation products, an assumption by no means excessive, espe- 
cially when we bear in mind the activity of the chemical changes 
which are going on during its life and growth. But if this step be 
taken, we cannot resist regarding the Amoeba in the same way ; its 
granules too are aggregation products, and the clear ectoplasm, 
when present, may be viewed as protoplasm in which aggregation is 
not occurring. The variations of amoeboid organisms in more or 
less granular character (a fact familiar to every observer) is thus 
brought into ob vious relation with the state of nutrition, or with the 
quality and quantity of external stimuli ; and its observed increase 
when stimulated, and its diminution during the resting state, are 
thus naturally accounted for. In the same way, in the granular 
pseudopodia of the Foraminifera, aggregation is in progress, in the 
hyaline processes of the Heliozoon not so. The granules of cells in 
higher animals m^ay be, at least to a very large extent, similarly 
explained ; while the disputes as to the presence or absence of a 
stroma become clearer when we bear in mind the fact that Darwin’s 
aggregation-masses are at least as often greatly elongated or spherical, 
and that they may run in any direction, and unite or separate to any 
extent. The remarkable differentiations of protoplasm visible during 
cell-division, as exhibited by ova (of course excluding yolk granules, 
&c.), may not improbably admit of the same explanation. 
3. Contractile Structures — Muscle . — The excessively difficult 
problem of muscular structure has not as yet received any widely- 
accepted solution, and even respecting matters of observation the 
widest discrepancies exist. In many invertebrates we cannot even 
be certain whether the muscles are striped or non-striped, so contra- 
dictory are the observations, while in a recent important paper by 
Professor Haycraf t,* the homogeneity even of striated muscle is main- 
tained. Brilliant light has, however, been lately thrown upon 
the arena of controversy by Professor Eutherford’s recent elaborate 
demonstration f that the discrepancies in observation are largely 
* Proc. Roy. Soc. Lond., 1881. 
t Proc. Roy. Soc. Edin., 1883. 
