CELLS IN LOWER PLANTS. 97 



cilia. The movements are of two kinds — viz., rotatory and 

 translatory, and these are so rapid as to make examination of 

 the living organism somewhat difficult. If a single organism be 

 examined microscopically, the following structure will become 

 apparent (see Fig. 74) : — 



i. A verv delicate outer membrane of cellulose, giviug the "blue " 

 reaction with Schulze's solution. 



ii. Internal to this, and separated from it by a considerable space, a 

 pear-shaped mass of cytoplasm, which may be teen to be composed of 

 a very thin layer of ectoplasm, and an internal endoplasm, in which 

 many Chlorophyll bodies are present. 



iii. Somewhere in the endoplasm the nucleus, a crescentic structure, 

 may possibly be detected ; but in the living cell this is not easy. 



iv. At the anterior end of the cell may be seen the tWO VlbratllC 

 cilia, which spring from the ectoplasm and pass through the outer mem- 

 brane of cellulose. 



V. Near the point of origin of the cilia, the red eye-SpOt can be 

 distinguished; the function of this body is not obvious, but that it can be 

 affected by light is not improbable. 



Delicate "bridles" of 03'toplasm stretch from the inner mass to the 

 internal surface of the outer membrane. 



If such a cell be treated with alcolwl, and then iodine, solution 

 be added, the pyrenoids will show up, a starch-ring being 

 present round each of these; only three or four pyrenoids are, 

 as a rule, present; the chlorophyll exists in the small chloro- 

 plasts in the endoplasm, and is extracted by the alcohol. 



The cilia are in reality hollow protrusions of the ectoplasm, 

 into which the endoplasm suddenly flows, only to withdraw 

 again with equal rapidity. During this process each cilium is 

 quickly bent in one direction, and straightened again, the sup- 

 position being that a cilium is thinner on one aspect than on the 

 opposite side. These sudden movements of the cilia have the 

 effect of moving the whole organism through the water, or of 

 producing rotatory movements. 



With the exception of A^^thalium (or the protozoan Amaba) 

 Sphmrella is the lowest form of plant cell which has been studied ; 

 in the case of such organisms, moreover, the animal kingdom is 

 closely approached, Sphcerella being very similar in structure to Noc- 

 tiluca (Protozoa). With regard to the distinction between a lower 

 plant and a lower animal organism the possession of chlorophyll 

 does not afford much help, as both plant and animal may possess 

 this pigment (c/. Hydra). The assimilation of carbon dioxide is, 

 however, a distinctive feature, starch being formed by plants, 



7 



