THE BUILDING-STONES OF THE ORGANIC WORLD 75 



or " cell " structure. In the resting nucleus the chromatin is 

 usually lying on the linin-threads in the form of granules. This 

 is particularly noticeable at the corners of the meshes. 



Of all the parts of the nucleus the chromatin requires the 

 most thorough consideration, for it is said to be the agent which 

 transmits the qualities of the parents through the germ-cells 

 to the children. We shall in another place consider at greater- 

 length the reasons which compel us to this assumption. That 

 the chromatin is a most important substance is proved by the 

 striking part played by it in the reproduction of the cell. 



Whether the nucleus is divided from the protoplasm by a 

 special membrane is a question which is at present undecided ; 

 probably different nuclei act in a different manner. 



It remains to mention a minute globule of a deep black 

 colour frequently found in the nucleus, the 'nucleus-corpuscle.' 

 What influence it has upon the life of the cell is at present 

 unknown, but as it is absent from many cells it is doubtful 

 whether any great importance is to be attached to it. 



Each cell contains usually only one nucleus, but we know 

 many vegetable and animal cells which contain two, three, and 

 even a hundred nuclei. 



Next to the nucleus we observe in most animal cells a little 

 strongly refractory granule surrounded by a halo. This is the 

 so-called centrosome which, according to many investigators, 

 represents the organ of locomotion. We shall deal with it in 

 detail when we come to consider the division of the cell. 



The organization of plant-cells differs from that of animal- 

 cells in that in the former we have to deal regularly with a 

 cell-wall or membrane secreted by the protoplasm. In addi- 

 tion the plant-cell contains the chlorophyll, which we have 

 already mentioned. It is these minute green corpuscles which 

 render it possible for all animal life on earth to exist, for only 

 they possess the faculty of changing inorganic matter into 

 organic compounds. 



Let us now endeavour to gain an insight into the function of 

 the single cell-parts. Though the layman will no doubt wonder 

 how it is possible to obtain accurate information from examining 

 such minute forms, he may rest assured that the task looks more 



