36 



PROTOZOA 



be learnt from an examination of Figs. XXIII., XXIV., XXV., 

 and the explanations appended to them. 



CLASS VI. ACINETAEIA, Lankester (Tentaculifera, Huxley). 



Characters. Highly specialized Corticate Protozoa, probably 

 derived from Ciliata, since their young forms are provided with a 

 more or less complete investment of cilia. They are distinguished 

 by having no vibratile processes on the surface of the body in the 

 adult condition, whilst they have few or many delicate but firm 



lG. XXVI. Acinetaria. 1. Ithyncheta cydopitm, Zenker. a, nucleus; 

 b, contractile vacuole ; only a single tentacle, and that suctorial ; x 150. 

 Parasitic on Cyclops. 2. Sphxrophrya urostylm, Maupas ; normal 



adult ; x 200. a, nucleus ; b, contractile vacuole. Parasitic in Urostyla. 

 3. The same dividing by transverse fission, the anterior moiety with tem- 

 porarily developed cilia, a, nucleus ; b, contractile vacuole. 4, 5, 6. 

 Sphxrophrya stentorea, Maupas ; x 200. Parasitic in Stentor, and at one 

 time mistaken for its young. 7. Trichophrya epistylidis, Cl. and L. ; 

 X 150. a, nucleus; 6, contractile vacuole. 8. Hemiophrya, gemmi- 

 para, Hertwig; x 400. Example with six Ijuds, into each of which a 

 branch of the nucleus a is extended. 9. The same species, showing 

 the two kinds of tentacles (the suctorial and the pointed), and the con- 

 tractile vacuoles b. 10. Ciliated embryo ol Podophrya Steinii, Cl. and 

 L.; x 300. 11. Acineta grandis, Saville Kent ; x 100 ; showing pedun- 

 culated lorica, and animal with two bunches of entirely suctorial tentacles. 

 a, nucleus. 12. Sphxrophrya magna, Maupas ; x 300. It has seized 



with its tentacles, and Is in the act of sucking out the juices of six examples 

 of the ciliate Colpoda parvifrons. 13. Podophrya elongata, Cl. and L. ; 



X 150. a, nucleus ; b, contractile vacuole. 14. Hemiophrya Benedenii, 

 Fraip. ; x 200 ; the suctorial tentacles retracted. 16. Vendrocometes 



rradoxui, Stein ; x 350. Parasitic on Gammaruz pulex. a, nucleus ; 

 contractile vacuole ; c, captured prey. 16. A single tentacle of 



Podophrya; x 800. (Saville Kent.) 17-20. Dendrosoma radians, Ehr.: 

 17, free-swimming ciliated embryo, x 600 ; 18, earliest fixed condition of 

 the embryo, X 600 ; 19, later stage, a single tentaculiferous process now 

 developed, x 600 ; 20, adult colony ; c, enclosed ciliated embryos ; d, 

 branching stolon ; e, more minute reproductive (V) bodies. 21. Ophryo- 



dendron pedicellatum, Hincks ; x 300. 



tentacle-like processes, which are either simply adhesive or tubular 

 and suctorial. In the latter case they are provided at their ex- 

 tremity with a sucker-disk and have contractile walls, whereas in 

 the former case they have more or less pointed extremities. The 

 Acinetaria are sedentary in habit, even if not, as is usual, per- 

 manently fixed by a stalk. The nucleus is frequently arboriform. 

 Reproduction is effected by simple binary fission, and by a modified 

 fission (bud-fission) by which (as in Reticularia and Arcella) a 

 number of small bud-like warts containing a portion of the branched 

 parental nucleus are nipped oft' from the parent, often simul- 

 taneously (Fig. XXVI. 8). These do not become altogether dis- 

 tinct, but are for a time enclosed by the parental cell each in a 

 sort of vacuole or brood-chamber, where the young Acinetarian 

 develops a coat or band of cilia and then escapes from the body of 

 its parent (Fig. XXVI. 10, 17). After a brief locomotive existence, 

 it becomes sedentary, develops its tentacles, and loses its cilia. 



The Acinetaria have one or more contractile vacuoles. Their 

 nutrition is holozoic. 



The surface of the body in some cases is covered only by a 

 delicate cuticle, but in other cases a definite membranous shell or cup 

 (often stalked) is produced. Freshwater and marine. See Fraipont 

 (89). 



ORDER 1. SUCTORIA, Kent. 



A greater or less proportion or often all of the tentacles are 

 suctorial and terminated with sucker-like expansions. 



Genera. Rhyncheta, Zenker (stalkless, naked, with only one 

 tentacle ; epizoic on Cyclops ; Fig. XXVI. 1) ; Urnula, C. and L. ; 

 Sphserophrya, C. and L. (naked, spherical, with distinctly capitate 

 tentacles only ; never with a pedicle ; parasitic within Ciliata, 

 supposed young ; Fig. XXVI. 2-6, 12) ; Trichophrya, C. and L. (as 

 Spheeroptirya, but oblong and temporarily fixed without a pedicle); 

 Podophrya, Ehr. (naked, solitary, globose, ovate or elongate, fixed 

 by a pedicle ; tentacles all suctorial, united in fascicles or distri- 

 buted irregularly; Fig. XXVI. 10, 13, 16) ; Hemiophrya, S. Kent (as 

 Podophrya, but the tentacles are of the two kinds indicated in the 

 definition of the group ; Fig. XXVI. 8, 9, 14); Podocyathus, S. Kent 

 (secreting and inhabiting stalked membranous cups or loricse ; ten- 

 tacles of the two kinds) ; Solenophrya, C. and L. (with a sessile 1 

 lorica ; tentacles only suctorial) ; Acineta, Ehr. (as Solenophrya, 

 but the lorica is supported on a pedicle ; Fig. XXVI. 11) ; Dendro- 

 cometcs, Stein (cuticle indurated ; solitary, sessile, discoid ; tentacles 

 peculiar, viz., not contractile, more or less branched, root-like, and 

 perforated at the extremities and suctorial in function ; Fig. 

 XXVI. 15). Dendrosoma, Ehr. (forming colonies of intimatel)' 

 fused individuals, with a basal adherent protoplasmic stolon and 

 upstanding branches the termination of which bear numerous capi- 

 tate suctorial tentacles only ; Fig. XXVI. 17-20). 



OEDER2. NON-SUCTORIA, Lankester ( = Actinaria, Kent). 



Characters. Tentacles filiform, prehensile, not provided with a 

 sucker. 



Genera. Ephclota, Str. Wright (solitary, naked, pedunculate, 

 with many flexible inversible tentacles) ; Actinocyathus, S. Kent ; 

 Ophryodendron, C. and L. (sessile, with a long, extensile, anterior 

 proboscis bearing numerous flexible tentacles at its distal extremity ; 

 Fig. XXVI. 21) ; Acinelopsis, Robin (ovate, solitary, secreting a 

 stalked lorica ; from the anterior extremity of the animal is deve- 

 loped a proboscis-like organ which does not bear tentacles). 



Further remarks on the Acinetaria. The independence of the 

 Acinetaria was threatened some years ago by the erroneous view of 

 Stein (79) that they were phases in the life-history of Vorticellidae. 

 Small parasitic forms (Sphferophrya) were also until recently 

 regarded erroneously as the " acinetiform young" of Ciliata. 



They now must be regarded as an extreme modification of the 

 Protozoon series, in which the differentiation of organs in a 

 unicellular animal reaches its highest point. The sucker-tentacles 

 of the Suctoria are very elaborately constructed organs (see Fig. 

 XXVI. 16). They are efficient means of seizing and extracting the 

 juices of another Protozoon which serves as food to the Acinetarian. 

 The structure of Dendrosoma is remarkable on account of its 

 multicellular character and the elaborate differentiation of the 

 reproductive bodies. 



The ciliation of the embryos or young forms developed from the 

 buds of Acinetaria is an indication of their ancestral connexion 

 with the Ciliata. The cilia are differently disposed on the young 

 of the various genera (see Fig. XXVI. 10, 17). 



