SCIENCE- GOSSIP. 



261 



along one of the borders a curious vesicle, quite 

 clear in appearance. This is probably only a 

 space in the endosarc, but, if watched, it will be 

 seen to vanish suddenly at intervals of about half 

 a minute ; then to slowly reappear and grow to its 

 full size. This vesicle is termed the " contractile 

 vacuole." It is important in being functional as 

 an excretory organ ; and if we watch carefully we 

 shall see close to the vesicle, near the border of the 

 body, one or more narrow slits through which the 

 fluid contents of the vesicle are suddenly expelled. 

 The waste products that are constantly being formed 

 by the oxidation of the protoplasm are being con- 

 tinually poured into the vesicle, which grows 

 during the process, and when full is forcibly con- 

 tracted. Moreover, at a certain spot at the side, the 

 ectosarc dips down into a sort of cavity, one side 

 of which is fringed with a number of processes 

 or cilia, comparable to those on the general 



Desmids are here partly dissolved, or partly thrown 

 out again, through the stomatal orifice. In the 

 accompanying figure two algal cells (probably 



Fig. 1. Paramoecium in Optical Section. 



a. Anterior end. p. Posterior end. to. Mouth, i. Desmids 

 undergoing digestion, one having just been taken in at mouth- 

 k. The contractile vacuole, x. Radial slits for passage outwards 

 of excretory products, h. Pood-particles, c. Cilia. 



surface of the body. This cavity forms the mouth, 

 or stomodaeum, of the organism. On viewing the 

 lateral surface we can discern that from this mouth 

 there proceeds a funnel-shaped depression that leads 

 into the endosarc. It is this depression that 

 forms the so-called pharynx, through which 

 particles of food or small organisms are introduced 

 into the interior. (See fig. 1.) 



The possession of a fringe of cilia along the 

 margins of the pharynx enables Paramoecium to 

 feed — i.e. capture small objects such as Desmids 

 or Diatoms. The manner in which this is brought 

 about is of especial interest. The cilia of the 

 fringe produce by their rapid to-and-fro move- 

 ments currents that sweep small particles and 

 large, lying near, right into the pharyngeal tube, 

 thence on into the endosarc. At the same time 

 the power is possessed of being able to reject such 

 matters as are not suitable for food, and these are 

 swept past the mouth with great rapidity. Once 

 in the pharynx the particle is forced down into the 

 internal protoplasm, where a process of digestion 

 goes on, aided, in all probability, by a certain 

 ferment manufactured by the protoplasm. The 

 hard external layers (cellulose) of such objects as 



Fig. 2. A Single Paramoecium fixed by Heat and stained 



WITH BOSIN AND MeTHYLBXE-BLUE TO DIFFERENTIATE 



the Nuclei from the Cell-body. 

 n. Macronucleus. n! . Micronncleus. m. Mouth. 



Desmideae) have just been taken in, and one is in 

 the act of entering the pharynx. 



The contractile vacuole ( 2 ) will on closer observa- 

 tion be seen to present certain stages during 

 growth to its full size, the first of these being one 

 in which .the vacuole possesses an elongated form, 

 then more spherical, until finally it becomes quite 

 circular in outline and suddenly bursts, the contents 

 being forced out through the slit that we have 

 already noticed. These contents are always quite 

 clear and fluid. From this it may be argued that 

 the nitrogenous, and perhaps some of the car- 

 bonaceous waste leaves the organism in solution 

 as ammonia and carbon dioxide, or at least in some 

 highly oxidised form. 



Paramoecium is one of those protozoans in which 

 occurs the method of reproduction known as 

 " rejuvenescence." Up to this point we have 

 made no mention of the "nuclei" that are 



Fig. 3. Diagrams illustrating the Action and Structure 

 01? a Oilium. 



(1) b. Base of oilium ; w. Thin-walled side. (2) Cilium hall- 

 bent by influx of endoplasm, indicated by arrow. (3) Cilium 

 nearly wholly bent. The dotted line indicates the extent to 

 which it will spring back. 



present in this organism, of which there are two — 

 a "macronucleus" and a " micronucleus." It is 

 the latter of these that is potential in reproduction ; 

 the former during rejuvenescence merely dis- 

 integrates and is absorbed, being probably of some 

 nutritive value. 



In rejuvenescence two individuals, of identical 



(2) There may be more than one vacuole present, but there is, 

 usually one large one. 



