OF THE PROTOZOA. 199 



Sect. III.— OF THE PROTOZOA. 

 (Plates XXI.-XXXI.) 



The term Protozoa, borrowed from two Greek words, protos, first or primi- 

 tive, and zoon, an animal, has of late been very generally adopted to signify 

 the simplest forms of animal life. Upon a review of these rudimentary 

 animals, it is at once perceived that they differ among themselves in organiza- 

 tion — that whilst some are amorphous and almost homogeneous, others exhibit 

 a degree of differentiation of parts, and the fii'st vestiges of internal organs to 

 carry on the processes of hfe ; again, it is seen that some have a distinct orifice 

 for the admission of food, or a mouth, which in others is absent, and, lastly, 

 that some with a definite figm^e are moved by vibratile cilia, whilst others 

 slowly progress by the alternate protrusion and retraction of ever- changing 

 and changeable processes derived from the general mass of their body. 



From a consideration of these structiural differences, one division of the 

 Protozoa is suggested into those moved by cilia, and those moved by variable 

 processes or ^ pseudopodes ' ; and a second, into those furnished with a mouth, 

 and those which are mouthless. We have accordingly constituted two pri- 

 mary divisions, viz., 1. Ciliata, Protozoa moved by cilia ; and 2. KJiizopoda, 

 moved by variable processes. The Rliizopoda (XXI.) are all mouthless, or 

 ^ astomatous,' whilst the Ciliata (XXIV.-XXX.) have a mouth, and are 

 styled by Siebold ' Stojnatoda,^ with the exception of a small family, the 

 Opalincea (XXII. 46, 47), and perhaps also of that of the Peridinicea 

 (XXXI. 16-23). 



However, besides the beings usually included among the Ciliata andi^A/zo- 

 poda, there are several subordinate Protozoic groups, some of which either 

 stand as it were midway between them, or represent a development of the 

 amoi-phous and mouthless Rhizopoda in a different direction ; such are the 

 Gregarinida (XXII. 28-36), with the associated Psorospermia (XXII. 37- 

 41), the Spongiada, Thalassicollida, and Polycystina, all which must rightly 

 also be numbered with the Protozoa. 



Of the Ciliata themselves, there is a fiu-ther and higher development of 

 their type in the subordinate groups of Ichthydina (XXII. 46-47) and Noc- 

 tilucida (XXXL), and, on the other hand, a degradation of it, as ah-eady 

 noted, in the case of the Opalincea and Peridinicea. Here we would remark 

 that the term ' Infusoria ' has been employed by several writers, in hen of 

 that of Ciliata, which we adopt ; still it is, to oui' mind, both less appropriate, 

 and also open to objection, not only on account of its meaning being quite 

 indefinite, but also by its having everywhere acquii'ed a very much wider 

 signification, in consequence of which it will always be open to misconception 

 when apphed to a comparatively very small class instead of, as heretofore, to 

 a very various and ^vide collection of microscopic organisms. Another word 

 invented is ' Stomatoda,' which is precisely equivalent in the extent of its 

 signification with the term Ciliata, the mouthless families only being excluded. 



Excepting their subordinate groups, the organisms comprehended among 

 the Ciliata and Rhizopoda formed, in conjunction with the Desmidiece, Dia- 

 tomece, and the families we have brought together imder the appellation 

 Phytozoa, the great class Polygastrica in the system of Ehrenberg. Little 

 reflection is necessary to convince ourselves of the very heterogeneous nature 



