INFUSORIA. 



[ 342 ] 



INFUSORIA. 



outside, but internally appears to pass gra- 

 dually into the softer substance of the central 

 mass, like the protoplasm in vegetable cells. 

 Like this again, it often appears to be pro- 

 longed in irregular processes across the 

 central mass, forming septa or cross parti- 

 tions, so that the softer substance occupies 

 only as it were cavities hollowed out in 

 the firmer reticular sarcodic mass ; hence 

 arises a cellular appearance. The existence 

 of the outermost coat or pellicle is demon- 

 strated by the phenomenon of ecdysis, which 

 occurs in certain species. But these mem- 

 branes or pseudo-membranes do not appear 

 to exist in all cases, for in some Infusoria the 

 body adheres readily to the glass of the 

 slider on which it is viewed under the micro- 

 scope, and is torn up into fragments in the 

 endeavour to free itself. 



The structure of these parts will be again 

 discussed in the sequel. 



Dr. Allman has lately pointed out the 

 occurrence of minute cilia-like filaments 

 attached at the base to cells (?) or rounded 

 bodies, imbedded in the integument, and 

 resembling the stinging organs of Hydra, &c. 



Locomotive organs. No distinct muscular 

 structure can be detected in the Infusoria, 

 but a contractile power is possessed by the 

 general substance of the body. In Vorticella 

 (PL 25. figs. 21 a & 27) and some others, 

 the contractile substance is prolonged 

 through the hollow pedicle, thus forming a 

 spurious muscular band. 



The other directly or indirectly locomotive 

 organs are thus distinguished. 1, cilia : 

 these are the most common, and form the 

 fine, short, very transparent, hair-like fila- 

 ments projecting from their surface. In 

 some they entirely cover the surface, whilst 

 in others they are arranged in one or more 

 rows round the mouth, or upon the ventral 

 surface, &c., as described under the genera. 

 During life they are seen actively vibrating, and 

 in some their motion appears constant; whilst 

 in others it is interrupted at intervals, appa- 

 rently under the influence of a will. They 

 are most distinctly seen when the Infusoria 

 are dried (see CILIA). 2, flagelliform fila- 

 ments (PI. 24. fig. 59) ; which are long 

 anterior cilia, the ends only of which are 

 vibratory and moveable in all directions ; 

 they are usually one or two only. 3, retract- 

 ing cilia or filaments (PI. 23. figs. 12, 18 a ; 

 PL 24. fig. 17) : these are single, long, 

 flexuous and directed backwards ; they fre- 

 quently become adherent to the slide, and 

 produce a sudden, backward motion of the 



animal. 4, setae or bristles (PL 24. fig. 53) : 

 these are rigid, filiform, straight and move- 

 able, but not vibratile, and are sometimes 

 provided with a bulb at the base ; they can 

 be slowly raised or depressed, and serve for 

 support, walking or climbing. 5, styles 

 (PL 25. fig. 17), are thick, straight, very 

 moveable setae, without bulbs ; they neither 

 rotate nor vibrate. 6, uncini or hooks (P1.41. 

 fig. 13) are short, thick, curved setae, serving 

 for prehension, climbing or creeping; and 

 are bulbous and usually very thick at the base. 



Nervous system. None has been dis- 

 covered. In the naked Infusoria, the sense 

 of touch is diffused throughout the substance 

 of the body. In others, it is particularly 

 developed in the snout-like appendages of 

 the body, and in the longer cilia, setae, &c. 

 The Infusoria are probably all sensible to 

 light, and many of them exhibit near the 

 anterior part of the body, one or more 

 coloured (mostly red) specks, which have 

 been considered as eyes ; but they contain 

 no distinguishable cornea, nor lens, nor are 

 they connected with any appreciable sub- 

 stance comparable to nervous matter; and 

 similar specks occur in the same situation in 

 the spores of many Algae; moreover, the 

 eye-specks are most distinct in those genera 

 which are doubtful Infusoria. Hence it might 

 be denied that they represent eyes. Yet 

 they bear considerable resemblance to the 

 eyes of the Rotatoria, and some Annelida; 

 so that their true nature must be considered 

 as problematical. 



Digestive system. On attentively exami- 

 ning Infusoria under a high power (1-4 to 

 1-8), a number of roundish spots are gene- 

 rally visible in the substance of the body ; 

 they are sometimes filled with a whitish 

 granular matter, at others they contain Des- 

 midiaceae, Diatomaceae, or other algae, or 

 bodies existing in the surrounding water. 

 These have been called gastric vesicles, cells, 

 spaces or sacculi. They are only visible 

 from their contents, and no membrane can 

 be distinguished in them. If a little indigo 

 or carmine be added to the water containing 

 the Infusoria, these cavities will soon become 

 filled and will be rendered very distinct ; in 

 the plates they are represented as filled with 

 these pigments. 



On attentively watching them, they will 

 appear to move around the body of the 

 animalcule, sometimes two of them appear- 

 ing to become fused into each other, or the 

 contents of one to pass into another. 



Finally, the pigment will be seen to escape 



