s. 



SCIENCE-GOSSIP. 



BRITISH INFUSORIA. 



By E. H. J. Schuster, F.Z.S. 



{Continual /row bagc 40.) 

 Part III. — Ciliata Holotkicha. 



'THE class Ciliata comprises those unicellular 

 animals which move by the vibrations of a 

 large number of small hair-like processes or cilia. 

 The most primary type of ciliate infusor is mon- 

 axial, bearing at one end a round mouth and at the 

 other end the anus. The whole surface is clothed 

 with rows of cilia of about the same length, which 

 run in a longitudinal direction. Two nuclear 

 bodies are present, the nucleus, meganucleus, or 

 endoplast, and the paranucleus, micronucleus, or 

 endoplastule. Of these the former seems to pre- 

 side over the nutrition, the latter over the repro- 

 duction of the animal. The body is enclosed in a 

 layer of firmer protoplasm known as the pellicle 

 or cuticle ; in this trichocysts are often present. 

 These organs are probably evolved for protective 

 purposes. In optical section they appear to be 

 small highly refractive rods. When the animal is 

 stimulated in certain ways they spring out suddenly 

 into long hairs which stand out from the sides of 

 the body. The application of a very dilute solution 

 of acetic acid or slight pressure on the cover-glass 

 produces this effect in such an animal as Para- 

 maecium aurelia . 



Departures from the primitive form arise in the 

 following ways : (1) by the prolongation of the 

 anterior portion of the body to form a necklike 

 process ; (2) by the shifting of the mouth from the 

 anterior end, either through this neck development 

 or from some other cause ; (3) by the excessive 

 development of one side of the body causing 

 asymmetry; (4) by differentiations of the primarily 

 homogeneous rows of cilia. This latter is, per- 

 haps, the most important modification, and it is 

 on the character and arrangement of the cilia that 

 all the various systems of classification are based. 



Stein divides the Ciliata into four orders, thus : 

 (1) Holotricha, in which the cilia do not differ much 

 in character and are evenly distributed ; (2) Hetero- 

 tricha, which possesses a specially developed adoral 

 band of cilia ; (3) Hypotricha, in which all the 

 cilia except the adoral band are confined to the 

 ventral surface ; (4) Peritricha, the cilia of which 

 are arranged in rings which encircle the body. 



Saville Kent follows Stein in his arrangement of 

 the orders, but changes about his families con- 

 siderably. O. Butschli, in volume i. of "Die 

 Classen und Ordnungen des Thierreichs," creates 

 two orders : into one he puts part of the Holotricha, 

 namely, those who have no undulating membrane 

 in the neighbourhood of the mouth and no cilia in 



the oesophagus : this he calls the Gymnostomata. 

 The other order contains the rest of the Ciliata, and 

 is called the Trichostomata. Although Butschli's 

 classification is, perhaps, the most natural, Saville 

 Kent's will be adopted here as I have used it in 

 speaking of the Flagellata. 



Family Paramaeciidae, defined by Saville Kent 

 thus : — " Animalcules free-swimming, more or less 

 flattened and asymmetrical, ciliate throughout ; oval 

 and cuticular cilia alike ; dorsal and ventral 

 surfaces distinct ; the oral aperture opening on the 

 ventral surface." 



Paramaecium auvelia Miiller, affords a good type 

 of the order Holotricha. The shape of the body is 

 like that of a slipper, and from this fact the 

 popular name, "slipper animalcule," is derived. 

 It is of large size, and is plainly visible with the 

 naked eye. On the left side, beginning near the 

 anterior end, is a triangular depression, which is 

 called the " peristome groove." From the apex of 

 the triangle leads a narrow tubular canal, the 



Fig. 20. — Paramaecium aurelia ( x 200.) 

 pg, peristome groove; os, oesophagus; tr, trichocysts un- 

 discharged; tv\ trichocysts discharged; cv, contractile 

 vacuoles; », nucleus ; n' paranucleus ; /, food vacuoles. 



" oesophagus." At the far end of this is the mouth. 

 The body is covered with a striated cuticle in 

 which trichocysts are evenly distributed. This is 

 clothed with rows of powerful cilia. When the 

 animal is alive, waves of contraction may be seen 

 to pass down these rows. Two contractile vacuoles 

 are present, one in the anterior, the other in the 

 posterior, half of the body. These are not simple, 

 but consist of a central round portion from which 

 spring five or six radial canals. These are said 

 to be connected by a branching system of ring 

 tubules with the whole of the body substance of 

 the animal. The central portion is connected 

 with the exterior by means of a small canal. 

 The vacuole seems to work as follows : water, 

 which probably contains the excreta in solution, 

 gradually collects in the radial canals ; these 



