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or Haeckel’s Protomyxa, is still disputed, nor is that of Ehizopods to 
Infusors, despite their more or less intermediate forms, as yet settled. 
But our current conceptions of the groups of Protista are based 
upon their more prominent and permanent characters only. An 
infusorian is constantly thought of as a permanently ciliated or 
flagellate organism ; a radiolarian is constantly described as a highly 
differentiated rhizopod, with two layers of protoplasm, a gelatinous 
envelope, yellow cells, and siliceous skeleton ; or again its simpler 
ally the heliozoon is seldom or never thought of without its radiat- 
ing pseudopodia with their peculiar axial filaments. 
Yet such conceptions involve a morphological fallacy of the most 
serious kind. These are indeed the most highly differentiated, the 
most frequent, the most permanent, and therefore the most striking 
forms in which these organisms are known to us, but of late years 
it has been becoming more and more obvious that each of these well- 
known forms is at best but the most important stage of a life-history, 
during which the organism passes through one or more other phases 
of form, which may indeed be transitory, but thereby lose no whit 
of their morphological distinctness or importance. 
Thus, thanks to the researches of Dallinger and Drysdale, 
Butschli, Savile Kent, and others,* we know that a monad is not a 
permanently flagellate form, but appears at one time encysted, at 
another becomes amoeboid ; the ciliated embryos of the Acinetse 
have long been known, f while more recent investigations have estab- 
lished the multiplication of radiolarians by zoopores, | or the frequent 
union of several individuals of various species of Heliozoa§ or of 
Gregarines|| into a single mass. In short, the progress of recent 
research among these forms has largely lain in revealing the exist- 
ence in even the most highly differentiated forms of a life-cycle of 
several distinct phases. 
In lower forms more attention is paid to the whole life-cycle, yet 
not sufficiently so. The Amoeba is still constantly spoken of as if 
its encysted stage were of no morphological interest, whereas no 
permanently amoeboid form has ever been proved by continuous 
* Savile Kent, Manual of the Infusoria. + Ihid. 
J Brandt, Monatsh. d. Berlin Akad., 1881. 
§ Gruber, Zool. Anzeiger, No. 118, 1882. 
II Gabriel, “ Z. Classif. d. Gregarinen,” Anzeiger, 1880. 
