40 



GENERAL EMBRYOLOGY 



sating vacuoles. Nutritive substances are often stored tem- 

 porarily in cells. These materials are collectively known as 

 deutoplasm, metaplasm, or paraplasm, and may be starch or 

 protein granules, yolk plates, oil drops, etc. There are also 



n. 



FIG. 18. "Trophospongien" in cells of the hepatic duct of the snail, Helix 

 pomatia. After Erhard. g, basal granules; n, nucleus; t, trophospongien. 



granules of various other kinds of materials being secreted 

 or excreted, of food in various stages of ingestion or digestion, 

 pigment granules, crystals, and formed substances of many 

 kinds, usually specific for the organism or tissue. 



In many cells true chromatic structures are found in the 



