OF THE PROTOZOA. EHIZOPODA. 201 



cysthia, and in singular relation with a spiciila skeleton in Sjpongiada and 

 TJialasskoUlda. 



So, if we look to the Ciliata, we find that the hardening of the superficial 

 lamina of their substance into a sort of integament gives rise to numerous 

 modifications in external form and fimctions, according to the degree of 

 induration, and the processes sent out. The flexible-skinned Colpodea 

 (XXIX. 25-50) depend for their movements upon their garnitiu-e of \-ibratile 

 cilia, and are merely swimmers, whilst the hard-coated Euplota (XXV. 350- 

 353) produce short moveable processes which act as legs, upon which they 

 can rapidly creep. Lastly, the selfsame primitive contractile substance is 

 formed into a stem in the Vorticella, which supports the animalcule at its 

 apex, and exhibits helicoid contractions, astonishing both by their rapidity 

 and completeness. 



SUBSECTION I.— EHIZOPODA. 

 (Plates XXI. XXII.) 



The true Wiizopoda constitute a large class of microscopic animated beings 

 of the most simple character. They may be defined as non-ciliated Protozoa 

 moving by variable expansions. Their organic animal substance presents no 

 distinction of tissues or of organs, but is homogeneous, contractile, and trans- 

 lucent, resembling a tenacious mucus or soft tremulous jelly, and is perpetually 

 changing its form by expanding itself at one or several points into processes 

 of ever-vaiying dimensions, arrangement, and number, and called in conse- 

 quence "" variable processes." Inasmuch, moreover, as these shifting offshoots 

 are their only means of locomotion, they have frequently been called " feet," 

 and, as they are also characteristic of the class, have given origin to the terms 

 *^ Pseudopoda " (with false feet) and " EMzopoda " (root-like feet) to desig- 

 nate it. Again, the lining mass is, in numerous instances, capable of enclos- 

 ing itself by a sheU of various figaire, consistence, and complexity ; and such 

 variations serve to separate the Ehizopoda into famihes and genera. 



In the simplest shell-less beings (XXI. 3, 4), vitality is exhibited by the 

 slow protnLsion and retraction of the variable processes, by the change of 

 form, their onward movement, and the introduction of nutritive substances, 

 and by the gradual changes of the introduced matters indicating a digestive 

 act. They therefore manifest vital contractility, a power of locomotion, a 

 degree of sensibility, and a digestive process. 



Eepeated observation likewise reveals the fact of progressive growth, and 

 the faculty of reproduction. The testaceous forms exhibit their \itality 

 after the same manner, and surpass the naked Ehizopoda only in the mar- 

 vellous power of secretion displayed in the production of their shells (XXI. 

 6-3G). 



Although in organization the Ehizopoda stand even below the ciliated 

 Protozoa, yet an animal natui'e must be allowed them ; indeed the simplest 

 forms are the rudest specimens of animal existence. Under the term RJiizo- 

 ptoda are comprised three well-marked families, viz. the Amcehina or Amoehcea, 

 which are without, and the Monothalamia and the Foraminifera, with shells. 

 The Monothalamia have one large opening to their monolocular (one-celled) 

 shells (XXI. 6-17) — hence the name, — whilst the Forambiifera owe theii^ de- 

 signation to the existence of numberless small orifices, generally distributed 

 over a multilocular (many-celled or chambered) testa (XXI. 20-36). 



We have frequently^ in the following pages, used the term ArceUina as 

 sjTionymous with Monothalamia ; for although the family known to Ehrenberg 

 under that name comprehended only a portion of the genera that Schultze 



