48 PROTOZOA chap. 



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

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

 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 Ehizopoda in the old wide sense (including all 



