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Proceedings of the Royal Society 
Be the latter suggestion valid or not, it is important to observe 
(1) that we have here (and for the first time so far as the writer is 
aware) an hypothesis which explains {a) the shortening and broad- 
ening of a contracting muscle, (h) its overcoming a mass resistance, 
in other words, that we have an explanation of the mode in which 
almost molecular movements are converted into movements of 
masses, a solution long sought by physiologists ; and (2), that this 
hypothesis depends simply upon the more or less fluid nature of the 
essential muscular components, and is entirely independent of the 
acceptance or rejection of the hypothesis of the preceding paper, 
which suggests the identification of these muscular components with 
aggregation granules. 
Explanation op Plate IV. 
In columns allotted to the four stages of the cell-cycle (encysted, cili- 
ated, amoeboid, and plasmodial) are arranged the corresponding phases 
of the form-history of a few typical Protozoa and Protophytes, as also a 
series of diagrams illustrating the normal and pathological form-history 
of the cells of higher plants and animals. All are thus seen to be refer- 
able to the Protomyxan or Myxomycete type. 
Among the Protozoa proper (figs. 3-8) the cell-cycle is almost com- 
plete ; the encysted and amcehoid stages are invari&ihly represented. The 
plasmodial phase is of frequent occurrence : in Infusorians, Gregarines, 
and Heliozoa that of multiple conjugation representing it, and demon- 
strating its essential continuity with conjugation, e.g.^ diatoms and algse 
(figs. 10-13), aiid even with fertilisation in plants and animals (figs. 
14 and 16). 
Fig. 18 shows the cell-cycle in a developing gastrula, e.g., sponge. In 
fig. 19 the various tissues are classified in relation to the cell-cycle ; the 
connective tissues to the encysted, the muscular to the amoeboid type, &c., 
even the plasmodial phase being represented during the histolysis of 
Polyzoa. Fig. 19 represents the development of an invertebrate amoeboid 
corpuscle, and fig. 20 its formation of a plasmodium when drawn, 
while figs. 20-25 continue the application of the same theory to the 
explanation of pathological change. 
