DEVELOPMENT. 37 



1. That it is a fluid homogeneous substance. 



2. That it consists of minute spherical globules, 

 like an emulsion. 



3. That it is a mass of interlacing fibrils, forming a 

 complex reticulum. 



In many cells the protoplasm, at or near the sur- 

 face, is quite dense, forming what is then called the 

 ectosarc. The more vicsid central portion is the 

 endosarc. 



In the cytoplasm, usually by the side of the nucleus, 

 a small body may be found in most cells, called the 

 centrosome. The centrosome is occasionally in the 

 nucleus and but little larger than a microsome, being 

 usually surrounded by a clear, radially striated area 

 of protoplasm called the attraction sphere. The cen- 

 trosome takes an active part in the multiplication of 

 cells, but otherwise its function is problematic. 



The cell wall is to be regarded as a cell product. 

 In plant tissues the cell wall is relatively thick and 

 composed largely of cellulose. In animal tissues the 

 cell wall is unusually thin, often difficult to demon- 

 strate, and in many cases absent. Examples of the 

 latter are amoebas, white blood corpuscles, nerve cells, 

 and probably liver cells. 



Nucleus. The nucleus is the second constituent 

 of the cell and is a round or an oval protoplasmic 

 body found floating in the cytoplasm. Its shape 

 usually corresponds to the form of the cell, but oc- 

 casionally C-shaped, ring-shaped, and even branched 

 nuclei are found. Its position may be eccentric or 

 at one end of the cell. It has more consistency than 

 the cytoplasm, but is plastic and displays consider- 



