PROTOPLASM 



14. Besides the protoplasm and the inert substances formed 

 by it, there are in many cases foreign substances to be found 

 within the various organs of an organism; 



such are, for example, the pebbles found in 

 the gizzard of certain birds,, the particles of 

 sand found in the antennal organ of the 

 crayfish, or the sand used by many minute 

 animals in forming a skeletal shell or test. 



15. Protoplasm is jelly-like in consis- 

 tency, and transparent, but not perfectly 

 homogeneous. Under the microscope it 

 is seen to consist of an infinitely large 

 number of minute particles of various sizes 

 and of different optical and chemical char- 

 acteristics. Chemical analysis shows that 

 it is highly complex; consisting largely of 

 carbon, oxygen, hydrogen and nitrogen, 

 with small quantities of sulphur, and occa- 

 sionally phosphorous, manganese, magnesium, calcium, sodium, 

 and chlorine. It is regarded as a more or less definite aggre- 

 gation of a large number of chemi- 

 cally complex bodies. 



1 6. In the smaller, microscopic 

 organisms the protoplasm may 

 usually be observed to consist of two 

 parts, nucleoplasm and cytoplasm. 

 The nucleoplasm, in the form of a 

 round or oval body, the nucleus, 

 occupies the centre of the mass and 

 is surrounded by the cytoplasm. 

 The nucleus and the surrounding 

 cytoplasm together are called a cell. 



In larger organisms there are a large number of nuclei quite 

 regularly distributed throughout the protoplasm. There are 



FIG. i. The test of 

 a protozoan, Difflugia, 

 composed of minute 

 grains of sand cemented 

 together. 



FIG. 2. Diagram of the cell. 

 For details see Fig. 179. 



