30 GENERA! SKETCH O I- THE CELL 



The most pressing of all questions regarding the cytoplasmic 

 structure is whether the sponge-like, fibrillar, or alveolar appearance 

 is a normal condition existing during life. There are many cases, 

 especially among plant-cells, in which the most careful examination 

 has thus far failed to reveal the presence of a reticulum, the cyto- 

 plasm appearing, even under the highest powers and after the most 







C D 



Fig. 13. Ciliated cells, showing cytoplasmic fibrillae terminating in a zone of peripheral 

 microsomes to which the cilia are attached. [ENGELMANN.] 



. /. From intestinal epithelium of Anodonta. B. From gill of Anodonta. ( '.'. /). Intestinal epi- 

 thelium of -Cy etas. 



careful treatment, merely as a finely granular substance. This and 

 the additional fact that the cytoplasm may show active streaming and 

 flowing movements, has led some authors, especially among bota- 

 nists, to regard the reticulum as non-essential and as being, when 

 present, a secondary differentiation of the cytoplasmic substance 

 specially developed for the performance of particular functions. It 

 has been shown, moreover, that structureless proteids, such as egg- 



