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observation to exist; in the Gregarine, on the other hand, the 
amoeboid state is often practically ignored by. classifiers. 
In the remarkable Protomyxa of Hseckel, however, we have an 
organism in which several phases of form are almost equally pro- 
minent, so that its description as an amoeboid, or a ciliated or as an 
encysted organism, has been alike impossible. For here is no per- 
manent highly differentiated form ; but an eventful life-history in 
which one protean mass of protoplasm passes through a cycle of 
several distinct phases. Let us careftdly examine then these phases, 
since light may thus be thrown upon the life-histories of the higher 
Protozoa already referred to. 
Starting then from the encysted stage, in which a mass of proto- 
plasm is surrounded by a dense envelope, we find that from this 
after a time (in which division of the protoplasm has in this case 
occurred), there issues a swarm of somewhat pear-shaped, naked, 
motile, flagellate organisms. After a brief period of active locomo- 
tion, these lose their flagellum and their permanent form alike, 
extrude pseudopodia, in short, melt down into amoebae. After 
some period of amoeboid life they flow together into a single proto- 
plasmic mass — unite into a plasmodium, as it is termed, and this 
after another brief but remarkable period of locomotion and pseudo- 
podial activity, settles down into a spheroidal mass ; this re-encysts 
itself, and the whole cycle commences anew (Plate IV. fig. 1). 
If now we make a diagrammatic representation of this life-history 
(or rather form-history, as it should more accurately be termed), of 
Protomyxa, exhibiting (1) the encysted, (2) the ciliated, (3) the 
amoeboid, and (4) the plasmodial stages, we shall find that all those 
temporary phases of form observed among the higher Protozoa may 
at once be referred to one or other of these (figs, 3, 8). If tljis be 
so, those curious phenomena of the exhibition of ciliated forms by 
organisms usually of amoeboid type like the Radiolarians, or of amoe- 
boid forms by organisms almost permanently encysted or motile, like 
Gregarines or Monads respectively, lose their anomaly, and come 
under a generalisation at once simple and comprehensive, viz,, 
that a form-history essentially similar to that of Protomyxa (with 
blanks it is true, but blanks which the progress of discovery is 
constantly filling up, and may not unlikely almost wholly fill), 
may be sketched out for all the higher Protozoa. The same idea 
