PLANT-CELLS 17 



of the beating, is brought about by some nervous mechanism 

 stimulated by the electric current, and the anaesthetic is 

 beheved. to do away with this nervous mechanism. Electric 

 currents which would cause the immediate dissolution, 

 histolysis, of a host of protozoa apparently have no effect 

 upon the mantle of the mollusc or its cilia after treatment 

 with anaesthetics. 



Cilia play so large a part in the life of higher animals that 

 it is a very extraordinary fact that two great groups of 

 multi-cellular animals are entirely devoid of them. The Round- 

 Worms or Nematoda, which are frequently parasitic in both 

 higher plants and animals, are devoid of cilia; and so is an 

 enormous group of animals which reaches the highest grade 

 of complexity and social organization, known as the Artiiro- 

 PODA. There are no cilia to be found in shrimps, lobsters, 

 crabs, in centipedes, spiders, mites or in insects. When one 

 considers the immense part cilia play in the life of all the other 

 great groups of animals one wonders that this great and 

 predominant class can get on without them. Cilia and flagella 

 are not so common in plants, but they exist in the male 

 reproductive cells in sea-weeds, mosses, ferns and even in 

 some primitive trees. 



Plant-Cells 



As a rule plant-cells are enclosed in a firm cell-wall, and 

 the name "cell" originates from the fact that when the 

 microscope was first discovered small slices of cork were 

 investigated, and cork consists of a series of the cases of 

 dead cells which are as regularly arranged as the cells in a 

 honeycomb. The living matter or protoplasm of plant-cells 

 is thus not naked, as it is in so many animal cells, but is en- 

 closed, as it were, in a suit of mail armour. But the proto- 

 plasm of one cell communicates by extraordinarih'- minute 

 channels with the protoplasm of neighbouring cells, and 

 further, this case or coating does not prevent the protoplasm 

 from moving. It often rotates within the cell-wall; it may be 

 flowing up both sides of the cell and returning down the 

 middle like a country dance, carrying with it various food 

 granules and at times the nucleus. 



S L 2 



