PROTOZOA 



13 



podia are lobose, ranging in form from mere wave-like bulgings 

 of the surface to blunt finger-like processes, but never having the 

 character of filaments either simple, arborescent, or reticulate. 

 Fusions of two individuals (conjugation) have been observed in a 



Kio. IV. Various Lobosa. 1, 2, 3. Dactylotphxra (Amoeba) polypodia, M. 

 Schultze, in three successive stages of division; tbe changes indicated 

 occupied fifteen minutes, a, nucleus ; b, contractile racuole (copied from 

 F. E. Schultze, in Architf. Mikrotk. Anat.). 4. Amoeba pritutpg, Ehr. 



(after Auerbach). a, nucleus ; 6, c, vacuoles (one or more contractile ; the 

 shaded granules are food-particles). 5. Pelomyxa patustris, Greeff 



(after GreefT), an example with comparatively few food-particles (natural 

 size ^,th inch in length). 6. Portion of a Pelomyxa more highly magni- 

 fied, o, clear superficial zone of protoplasm (so-called " exoplasni ") ; b, 

 vacuoles, extremely numerous ; e, lobose pseudopodium ; d, a similar 

 pseudopodium ; , nuclei ;/, "refractive bodies "(reproductive?) ; scattered 

 about in the protoplasm are seen numerous cylindrical crystals. 7. 



ArceUa vulgarif. Ehr. a, shell; 6, protoplasm within the shell ; c, extended 

 protoplasm in the form of lobose pseudopodia ; d, nuclei ; t, contractile 

 vacuole ; the dark bodies unlettered are gas vacuoles. 8, Codilio- 



podium ptUucidum, Hert. and Less, a, nucleus surrounded by a hyaline 

 halo sometimes mistaken for the nucleus, whilst the latter is termed 

 nncleolus. 



few cases, hut not fusions of many individuals so as to form 

 plasmodia ; nevertheless the size attained by the naked protoplasm 

 by pure growth is in some cases considerable, forming masses readily 

 visible by the naked eye (Pelomyxa). The presence of more than 



one nucleus is a frequent character. A contractile vacuole may or 

 may not be present The formation of sporocysts and of chlamydo- 

 spores (coated spores) has not been observed in any species, but 

 naked spores (Hagellulae or amcebulae) have been with more or 

 less certainty observed as the product of the breaking up of some 

 species (Amoeba ? Pelomyxa). The cyst phase is not unusual, but 

 the cyst appears usually to be a hypnocyst and not a sporocyst 

 In the best observed case of spore-production (Pelomyxa) the spores 

 were apparently produced without the formation of a cyst. Repro- 

 duction is undoubtedly most freely effected by simple fission 

 (Amoeba) and by a modified kind of bud-fission (Arcella). Fresh- 

 water and marine. Two orders of the Lobosa are distinguished in 

 accordance with the presence or absence of a shell. 



ORDER 1. NUDA. 



Characters. Lobosa devoid of a shell. 



Genera. Amceba, Auct (Fig. IV. 4) ; Ouranueba, Leidy (with a 

 villons tuft at one end, Wallich's A. villosa) ; Corycia, Dnj. (low, 

 ridge-like pseudopodia); Lithamceba, Lankester (Fig. V.); Dina- 

 macba, Leidy (92) (covered with short stiff processes) ; Eyalodiseus, 

 H. and L. ; Plakopus, F. E. Schultze ; Dactyloxph&ra, H. and L. 

 (Fig. IV. 1, 2, 3); Pelomyxa, Greeff (Fig. IV. 5, 6) ; Amphizonella, 

 Greeff (forms a gelatinous case which is broken through by the 

 pseudopodia). 



ORDER 2. TESTACEA. 



Characters. Lobosa which secrete a shell provided with an 

 aperture from which the naked protoplasm can be protruded. The 

 shell is either soft and membranous, or strengthened by the in- 

 clusion of sand-particles, or is hard and firm. 



Genera. CocMiopodium (Fig. IV. 8), H. and L. ; Pyxidictila, 

 Ehr. ; Arcella, Ehr. (Fig. IV. 7) ; Hyalosphenia, Stein ; Quad- 

 rula, F. E. Schultze (shell membraneous, areolated) ; Difflugia, 

 Leclerc (shell with adventitious particles). 



Further remarks on the Lobosa. The Lobosa do not form a very 

 numerous nor a very natural assemblage. Undoubtedly some of 

 the forms which have been described as species of Amoeba are 

 amoeba forms of Mycetozoa ; this appears to be most probably the 

 case in parasitic and stercoricolous forms. But when these are 

 removed, as also those Proteomyxa which have pseudopodia of 

 varying character, at one time lobose and at another filamentous, 

 we have left a certain small number of independent lobose 

 Gymnomyxa which it is most convenient to associate in a 

 separate group. We know very little of the production of spores 

 (whether it actually obtains or not) or of developmental phases 

 among these Lobosa. The common Amoeba are referable to the 

 species A. princeps, A. lobosa, Daetylosphsera polypodia, Ouramasba 

 rillosa. Of none of these do we know certainly any reproductive 

 phenomena excepting that of fission (see Fig. IV. 1, 2, 3). Various 

 statements have been made pointing to a peculiar change in the 

 nucleus and a production of spores having the form of minute 

 Amoebas, arising from that body ; but they cannot be considered 

 as established. Whilst the observed cases of supposed reproduc- 

 tive phenomena are very few, it must be remembered that we have 

 always to guard (as the history of the Ciliata has shown, see 

 below) against the liability to mistake parasitic amabnlae and 

 flagellnlae for the young forms of organisms in which they are 

 merely parasitic. The remarkable Pelomytn palustris of Greeff (32) 

 was seen by him to set free (without forming a cyst) a number of 

 amoebulae which he considers as probably its young. Mr Weldon 

 of St John's College, Cambridge, has observed the same pheno- 

 menon in specimens of Pelomyxa which made their appearance in 

 abundance in an aquarium in the Morphological Laboratory, 

 Cambridge. It seems probable that the amcebulse in this case are 

 not parasites but spore-like young, and this is the best observed 

 case of such reproduction as yet recorded in the group. 



Arcella is remarkable for the production of bud-spores, which 

 may be considered as a process intermediate between simple fission 

 and the complete breaking up of the parent body into spores. As 

 many as nine globular processes are simultaneously pinched off from 

 the protoplasm extruded from the shell of the Arcella ; the nuclei 

 (present in the parent Arcella to the number of two or three) have 

 not been traced in connexion with this process. The bnds then be- 

 come nipped off, and acquire a shell and a contractile vacuole (33). 



The presence of more than one nucleus is not unusual in Lobosa, 

 and is not due to a fusion of two or more uninuclear individuals, 

 but to a multiplication of the original nucleus. This has been 

 observed in some Amoebae (A. princepsl) as well as Arcella. 

 Pelomyxa (Fig. IV. 6) has a great number of nuclei like the Helio- 

 zoon, Actinosphaerium (Fig. VIII.). 



Pelomyxa is the most highly differentiated of the Lobosa. The 

 highly vacuolated character of its protoplasm is exhibited in a less 

 degree by Lithamceba and resembles that of Heliozoa and Radiolaria. 

 Besides the numerous nuclei there are scattered in the protoplasm 

 strongly refringent bodies (Fig. IV. 6, /), the significance of which 

 has not been ascertained. The superficial protoplasm is free from 

 vacnoles, hyaline, and extremely mobile. Occasionally it is drawn 



