182 INTRODUCTION TO CYTOLOGY 



tered in animals as well as in plants. Zoologists have differed widely in 

 their interpretations of the "intercellular substance" composing such 

 membranes in animal tissues. Heidenhain and Rohde have emphasized 

 the view that this substance is metaplasm, a special form of living sub- 

 stance which differentiates in protoplasm in connection with special 

 functions and which is capable of growth, response to certain stimuli, and 

 further differentiation. A. Meyer has strongly opposed this conception, 

 holding that the albuminous intercellular substance of animals, like the 

 carbohydrate wall of plants, is ergastic in nature and not to be classed 

 with metaplasmic (alloplasmatic; Meyer) differentiations. The fibrils 

 frequently observed in the intercellular substance, which many have taken 

 as indications of its metaplasmic nature, Meyer regards as modifications 

 of the ergastic material or as substances which have arisen in protoplasmic 

 connections.^^ 



The membranes of animal cells differ from those of most plants in 

 consisting largely of such substances as chitin, elastin, keratin, and gelatin 

 rather than cellulose and related carbohydrates. Cellulose has been 

 found only rarely among animals. In the ascidians, as has long been 

 known, the outer layer of the body wall consists largely of cellulose. A 

 cellulose-like substance has recently been found in the skeletal plates 

 of an infusorian (Dogiel, 1923a). 



28 Heidenhain (1902, 1907), Rohde (1908, 1914, 1923), Meyer (1896, 1920); see 

 also p. 45. See the general account by Studnicka (1925). 





