LECTURE I. 



INTRODUCTORY. 



IF a drop of the rain-water which has collected in a water- 

 butt be examined under the microscope, a number of minute 

 somewhat pear-shaped bodies of a green colour will be seen 

 actively swimming in it. These bodies are what are termed 

 the zoospores of a small Alga, H&matococcus pluvialis, better 

 known as Protococcus. The rapidity of the movements of 

 these bodies makes it difficult to observe their structure, but, 

 if a trace of iodine be added to the drop of water, they will 

 be brought to rest. It will then be seen that they are not 

 all quite alike, some being smaller and others larger. The 

 smaller ones consist of a minute mass of a jelly-like substance, 

 granular and coloured green for the most part, but clear and 

 colourless at the more pointed end where it is prolonged into 

 two delicate filaments termed cilia : the larger ones have the 

 same structure, but they possess in addition a membrane 

 through which the cilia protrude (Fig. I. A.). To this jelly- 

 like substance the name of protoplasm has been given, and, 



FIG. T. A, Zoospore of Hcematococcus pluvialis : B, Hsematococcus cell. 



V. I 



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