CELLS AND NUCLEL 265 



An amoebiform or amoeboid cell consists only of cell-sub- 

 stance enclosing a nucleus ; it possesses the property of spon- 

 taneous movement by means of pseudopodia, like an amoeba, 

 and is capable of ingesting solid and fluid materials, which 

 appear as globules or granules in its interior. 



Many mature cells have a large quantity of granular material, 

 and others have oil, as, for example, the fat cells, stored in their 

 protoplasm — Cell contents. Such stored material is usually 

 formed by the cell, and is sometimes present in so large a quantity 

 that the cell-substance forms a mere wall around the contents. 

 It is from this form of cell, which was first discovered, that the 

 appellation has been extended to all cells. It has therefore 

 acquired a new and technical meaning. 



Non-amoeboid cells are usually called ' fixed,' and are 

 frequently surrounded by a distinct film, or cell-wall, either 

 secreted by or formed from the protoplasm of the cell. The 

 cells in Insects are united either by the fusion of their proto- 

 plasm, when the spongioplasm of one cell may be traced into 

 those adjacent to it, or by an intercellular cement material, and 

 rarely by a more copious matrix. 



Mucoid Degeneration. — The part of the protoplasm of a 

 cell which is exposed, either by reason of the cell forming 

 a portion of the surface of the body, or of the lining of 

 the alimentary canal, is sometimes observed to become clear 

 and transparent, and to stain very feebly or not at all. This 

 part of the cell consists of mucin, or of that modification of 

 mucin termed chitin. It is the result of a change in the 

 character of the cell substance itself, and, as this material 

 exhibits none of the vital properties characteristic of proto- 

 plasm, its formation may be regarded as a kind of degenera- 

 tion. 



The great cells of the fat bodies of Insects are surrounded by 

 a thin pellicle of chitin, which forms the cell-wall. 



Whether the mucin or chitin formed by cells is to be re- 

 garded as an excretion or as a modification of the cell substance 

 has long been a matter of speculation. From the changes 

 which occur in the cells of Insects, I have no hesitation in 



18—2 



i-> 



