5 2 PROTOZOA 



Ehr. ; Difflugia, Lecleroq; Lecqueureusia, Schlnmberger ; Hyalosphenia, 

 Stein; Quadrula, F. E. Sch.; Heleopera, Leidy ; Podostoma, CI. and L. ;. 

 Arcuothrix, Hallez. 

 II. Ectoplasm undifferentiated, containing moving granules ; pseudoiaodia 

 branching freely towards the tips .... Filosa 



Euglypha, Duj. ; Paulinella, Lauterb. ; Cyphoderia, Schlumb. ;: 

 Gampascus, Leidy ; Chlamydophrys, Cienk. ; Gromia, Duj. = Hyalopus, 

 M. Sch. 



We have defined this group mainly by negative characters, as 

 such are the only means for their differentiation from the remain- 

 ing Sarcodina ; and indeed from Flagellata, since in this group 

 zoospores are sometimes formed which possess flagella. More- 

 over, indeed, in a few of this group {Podostoma, Arcuothrix), as 

 in some Heliozoa, the flagellum or flagella may persist or be 

 reproduced side by side with the pseudopodia. The subdivision of 

 the Ehizopoda is again a matter of great difficulty, the characters 

 presented being so mixed up that it is hard to choose : however, 

 the character of the outer layer of the cytoplasm is perhaps the 

 most obvious to select. In Lobosa there is a clear layer of 

 ectosarc, which appears to be of a greasy nature at its surface 

 film, so that it is not wetted. In the Filosa, as in most other 

 Sarcodina, this film is absent, and the ectoplasm is not marked 

 off from the endoplasm, and may have a granular surface. Corre- 

 sponding to this, the pseudopodia of the Lobosa are usually 

 blunt, never branching and fraying out, as it were, at the tip, 

 as in the Filosa ; nay, in the normal movements of Amoeha limao: 

 (Fig. 1, p. 5) the front of the cell forms one gigantic pseudopodium, 

 which constantly glides forward. Apart from this distinction 

 the two groups are parallel in almost every respect. 



There may be a single contractile vacuole, or a plurality ; or 

 none, especially in marine and endoparasitic species. The nucleus 

 may remain single or multiply without inducing fission, thus 

 leading to apocytial forms. It often gives off "chromidial" 

 fragments, which may play an imporbant part in reproduction.'^ 

 In Amoeba hinucleata there are constantly two nuclei, both of which 

 divide as an antecedent to fission, each giving a separate nucleus 

 to either daughter-cell. Pelomyxa palustris, the giant of the group, 

 attaining a diameter of 1'" (2 mm.), has very blunt pseudopodia, 

 an enormous number of nuclei, and no contractile vacuole, though 



' The significance of chvomidia in Sarcodina (first noted by Sohaudinn in Fora- 

 minifera) was fully recognised and generalised by R. Hertwig in Arch. Protist, 

 i. 1902, p. 1. 



