188 



GENERAL PHYSIOLOGY 



1. Growth and Reproduction 



Reproduction cannot be separated from growth, for in the 

 widest sense it is only a special case of growth; the earlier 

 embryology was prompted to regard reproduction as growth beyond 

 the measure of the individual. The general process that consti- 

 tutes growth is an increase of living substance, and the essence of 

 reproduction likewise consists merely in an increase of living sub- 

 stance. The difference between that which is usually termed 

 growth in the narrow sense and the phenomenon of reproduction 

 consists only in the fact that in the former case the newly formed 



FIG. 67. SUntor polymorplms. N, Monilifonn nucleus ; o, mouth-opening, cv, contractile vacuole. 

 /. Young individual extended. II. Older individual in the process of division, contracted. 

 (After Stein.) 



living substance remains in constant connection with the original 

 organism and helps to increase its volume ; while in the latter case 

 a part of the substance separates itself from the original organism, 

 either, as in most cases, being set entirely free, or, as in the increase 

 of tissue-cells, being separated merely by a partition- wall and re- 

 maining in place. Correspondingly, there is a large number of 

 transitions between the growth, in the narrow sense, and the 

 reproduction of the cell. Examples of such are afforded especially 

 by many multinucleated cells, as, e.g., Opalina,the infusoriari living 

 in the intestine of the frog, which at first is uninucleated and in 

 growth becomes multinucleated by the repeated division of its 

 nucleus. There occurs here a reproduction of the nuclei, while the 



