48 PROTOZOA CHAP. 



bution," just as with the fresh-water Turbellaria and the Eotifers 

 (vol. ii. pp. 4 f., 226 f.). We can distinguish in fresh- water, as in 

 marine Protista, " littoral " species living near the bank, among 

 the weeds; "plankton," floating at or near the surface; "zonal" 

 species dwelling at various depths ; and " bottom-dwellers," mostly 

 " limicolous " (or " sapropelic," as Lauterborn terms them), and to 

 be found among the bottom ooze. Many species are " epiphytic " 

 or " epizoic," dwelling on plants or animals, and sometimes choice 

 enough in their preference of a single genus or species as host. 

 Others again are " moss-dwellers," living among the root-hairs 

 of mosses and the like, or even " terrestrial " and inhabiting 

 damp earth. The Sporozoa are internal parasites of animals, 

 and so are many Flagellates, while many Proteomyxa are 

 parasitic in plant-cells. The Foraminifera (with the exception 

 of most Allogromidiaceae) are marine, and so are the Eadiolaria ; 

 while most Heliozoa inhabit fresh water. Concerning the dis- 

 tribution in time we shall speak under the last two groups, the 

 only ones whose skeletons have left fossil remains. 



Classification. — The classification of the Protozoa is no easy 

 task. We omit here, for obvious reasons, the unmistakable 

 Plant Protists that have a holophytic or saprophytic nutrition ; 

 that are, with the exception of a short period of locomotion in 

 the young reproductive cells, permanently surrounded with a 

 wall of cellulose or fungus-cellulose, and that multiply and grow 

 freely in this encysted state : to these consequently we relegate 

 the Chytkidieae, which are so closely allied to the Proteomyxa 

 and the Phycomycetous Fungi ; and the Confervaceae, which in 

 the resting state form tubular or flattened aggregates and 

 are allied to the green Flagellates ; besides the Schizophyta. 

 At the opposite pole stand the Infusoria in the strict sense, 

 with the most highly differentiated organisation found in our 

 group, culminating in the possession of a nuclear apparatus with 

 nuclei of two kinds, and exhibiting a peculiar form of conjugation, 

 in which the nuclear apparatus is reorganised. The Sporozoa are 

 clearly marked off as parasites in living animals, which mostly 

 begin life as sickle-shaped cells and have always at least two 

 alternating modes of brood-formation, the first giving rise to 

 aplanospores, wherein is formed the second brood of sickle- 

 shaped, wriggling zoospores. The remainder, comprising the 

 Sarcodina, or Rhizopoda in the old wide sense (including all 



