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General Biology 



that there is an "internal reticular apparatus" consisting of a system of 

 rods or network close to the nucleus, but associated especially with the 

 dense protoplasm which surrounds the centrosome. In epithelial cells 

 the network lies close to the free ends of the cells. The Golgi apparatus 

 is probably found in all animal cells, though little is as yet known about 

 it, except that there is a continuity from parent-cell to daughter-cells 

 by a sort of mitotic division of it quite similar to the regular chromosome 

 division. Prolonged treatment with osmic acid will make the Golgi 

 apparatus visible. 



Plastids are differentiated portions of protoplasm representing cer- 

 tain regions in which physiological processes are localized. They are 

 quite common in plants and protozoa. In the former they are usually 

 colored, such as the chloroplasts which are the chlorophyl-carrying 

 organs. Each kind of plastid is supposed to serve a separate type of 

 function. 



Attraction sphere and Centrosome. These may be quite conspicuous 



Fig. 28. Golgi Apparatus in Epidermal Cells. 



a. Golgi network beside the nucleus in cell of a horse. 



b. Same in skin of cat, but broken into small rods around the mitotic figure 

 in the large central cell. (After Deinecka.) 



although it is not known whether they are important or not in cell- 

 division, shortly to be described. 



Paraplasmic substances. These are the foreign substances which 

 can be seen in the cytoplasm, but which have not become part of the 

 living cell itself. Such are granules of pigment or calcium, fat globules, 

 various vacuoles filled with fluid, etc. 



"It is clear," says a recent writer, "that the construction of the cell 

 is highly specialized in most cases for the function which it is to carry 

 out, and that it is supplied with the most perfect mechanisms for these 

 purposes. Some of these are evident in the form of contracted bands 

 in the protoplasm, or in long, nerve processes ( ) 



like electric wires carefully insulated by sheaths of fatty material, or in 

 mobile cilia which mechanically perform duties in the transportation 

 of foreign particles. In others, the tools of their trade are recognizable 



