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streaks and granules of a more highly refracting and more fluid sub- 
stance in which the colouring matter when present become accumula- 
ted!. Darwin extended these observations to the protoplasm of root- 
cells and indicated its wide prevalence throughout the vegetable 
kingdom, and the object of the present paper is to extend and apply 
these observations still further. 
On this view the granules of an Amoeba or Torula are (disregard- 
ing of course sap-vacuoles and fat globules) aggregation products, 
the clear ectoplasm when present being merely a portion of the homo- 
geneous protoplasm in which aggregation is not occurring. The more 
or less granular character of the Amoeba would thus depend on the 
state of nutrition and the quality and quantity of external stimuli, and 
would naturally be least evident in the resting state. In the granular 
pseudopodia of a Foraminifer aggregation is in progress, in those of the 
Heliozoon not so. The granules of cells in higher animals may be simi- 
larly explained, while the opinion of Klein and other histologists, that 
the granules are the optical expressions of the intersections of a stroma 
or network of more highly refracting filaments traversing the proto- 
plasm, may be correlated with this view when we remember that Dar- 
win’s aggregation masses are as frequently linear as spherical and that 
they may run in any direction. 
The radiate arrangement of granules visible during the maturation 
and impregnation of so many ova I regard as again dependent upon 
aggregation, while even the striae in the division of the nuclear spindle 
seem to be of essentially similar nature. 
In the insectivorous plant too it is clear that this process of 
aggregation is closely associated with contractility, but no movement 
can of course ensue; in the Amoeba however where no cell-wall im- 
pedes motion the irregular aggregation is accompanied by irregular 
contractility and this necessarily by changes of external form. The very 
mechanics of such movement becomes intelligible, for the surface ten- 
sions of an elongated aggregation-mass tend to draw it into spherical 
form even against resistance. It is inevitable to apply such an hypo- 
thesis to the specialised contractile tissue. In many Invertebrates one 
observer has described the muscles as striated, the next as homogene- 
ous, and even respecting such permanently striated muscle as that of 
the Vertebrates the wildest discrepancies exist. 
Rutherford? in what seems to be the most important paper in 
1 These observations were corroborated by Francis Darwin (Quarterly Journal 
Microscop. Science XVI), who showed that the granules did not consist of sap as 
some had supposed but were essentially protoplasmic in nature. 
2 On the Structure of Arthropod Muscle. Proc. Roy. Soc. Edinburgh 1883. 
