INFUSORIA. [ 



variable number of new individuals, discharged 

 by the bursting of the parent- cyst ; or (b) 

 new individuals are formed singly or in small 

 numbers by a process of internal budding, 

 the new individuals becoming free within 

 the parent, and then escaping from the cyst; 

 or (c) the simple encysted form is metamor- 

 phosed into the Acineta (free) or Podophrya 

 (stalked) form, by the protrusion of tuber- 

 cular processes ; in this state it gives origin 

 to new individuals by internal budding (from 

 the nucleus). Colpoda afford examples of 

 the processes 1 and 2, a and b ; the Vorti- 

 cellte of all three together, with the two 

 modifications of 2 c. 



When the Vorticellcs are about to become 

 encysted, they draw in their ciliated disk and 

 contract their bodies into a ball, at the same 

 time secreting around them a gelatinous mass 

 which solidifies into a firmer elastic covering. 

 Sometimes this occurs whilst adherent to the 

 stalk, which latter then soon dies away and 

 disappears, this process being first indicated 

 by the breaking up of the muscular band 

 into separate portions. More frequently, 

 however, it becomes detached from the stalk 

 first, and a ring of cilia is developed near the 

 end of the body of the Vorticella, which be- 

 comes encysted whilst swimming. The Aci- 

 neta or Podophrya forms are further metamor- 

 phoses of the gelatinously encysted forms. 



Conjugation. A process of union of the 

 bodies of distinct individuals has been ob- 

 served in the Infusoria, in the ordinary 

 forms as well as in the Acineta and Podo- 

 phrya conditions (PI. 25. fig. 33). So far as 

 the point is ascertained, however, this phae- 

 nomenon does not seem to be connected 

 with reproduction. The blending of the 

 individuals does not become complete ; it is 

 rather a cohesion, and the lines of demarca- 

 tion may always be traced. Three, four, or 

 even more have been observed united 

 together. Conjugating pairs might be taken 

 for a dividing body if hastily viewed. But 

 the distinction is not only perceptible by the 

 reverse order of the changes seen on watching 

 the object, the bodies becoming more and more 

 blended instead of separated, but the frequent 

 diversity in the condition of the bodies, as to 

 transparency, &c., and above all, the nuclei, 

 clearly mark the characters. The nucleus 

 of a dividing body is ordinarily extended 

 longitudinally at right angles to the line of 

 division, being divided across by this. In 

 conjugation the two nuclei are generally 

 found lying parallel to each other and (at 

 some distance) to the surface of union. 



16 ] INFUSORIA. 



Some observers have attempted to prove 

 that Infusorial animals and plants are derived 

 from the direct transformation of organic 

 matters ; thus the molecules of the ultimate 

 fibrilla3 of muscle, when separated by the 

 effect of decomposition, acquire the appear- 

 ance and motion of Bacteria. These obser- 

 vations, however, prove nothing to the point, 

 because the bodies are so much alike as to 

 be undistinguishable by mere appearance, 

 and without the use of chemical reagents. 

 These have been entirely neglected. Repe- 

 tition of the experiments with the aid of 

 acetic acid and solution of potash, shows 

 readily that these notions are entirely erro- 

 neous. 



When we consider that the multiplication 

 of the Infusoria by division takes place 

 according to a geometrical progression, also 

 that they need only become encysted to 

 produce swarms of germs, we can easily 

 understand their rapid propagation in liquids; 

 when also they will resist a degree of cold 

 = 8 F,, and an elevated temperature of 

 260 F., or even desiccation, without destruc- 

 tion, and when their minute size is added, 

 we can readily understand their almost uni- 

 versal diffusion. 



As we have stated, a drop of water can 

 scarcely be found which does not contain 

 some Infusoria. Many of them will only 

 live in fresh or sweet water, whilst others 

 are found only in decomposing and even 

 putrid water containing decomposing animal 

 and vegetable substances ; others, again, are 

 only met with in salt or brackish water. 

 Those existing in fresh water may be col- 

 lected in ordinary wide-mouthed bottles, 

 a drop of which may be removed by the 

 dipping-tube ; any individual one perceptible 

 to the eye may be withdrawn by the same 

 means. Their natural movements are best 

 watched in the live-box; but these move- 

 ments greatly interfere with the observance 

 of the contractile vesicles, and general mi- 

 nute structure, which is best seen when they 

 are simply confined between the slide and 

 cover, in a small quantity of water. A good 

 plan for arresting their motions is that of 

 warming the slide containing them over a 

 candle or lamp for a short time. Many In- 

 fusoria live only in particular kinds of infu- 

 sions, just as certain plants live only upon 

 particular kinds of soil ; and these infusions 

 should be prepared by adding cold fresh 

 water to the vegetable or animal substances, 

 the water being in considerable excess, and 

 allowing the mixture to remain for a time. 



