206 LIFE AND DEATH. 



crustaceae; and finally in the destruction and the 

 neo-formation of the globules of the blood of verte- 

 brates, of the glandular cells, and of the epithelial 

 cells of the intestine. 



Accidental Regeneration in Protozoa and Plastids. — 

 There is also an accidental regeneration which more or 

 less perfectly renews the parts that are lost. This 

 regeneration has its degrees, from the simple cicatriza- 

 tion of a wound to the complete reproduction of the 

 part cut off It is very unequally developed in 

 zoological groups even when they are connected. 

 In the elementary monocellular beings — i.e., in the 

 anatomical elements and in the protozoa, — the experi- 

 ments in merotomy, i.e., in partial section, enable us 

 to appreciate the extent of this faculty of regenera- 

 tion. These experiments, inaugurated by the re- 

 searches of Augustus Waller in 1851, were repeated 

 by Gruber in 1885, continued by Nussbaum in 1886, 

 Balbiani in 1889, Verworn in 1891, and have been 

 reproduced by a large number of observers. They 

 have shown that the two fragments cicatrize, and are 

 repaired, building up an organism externally similar 

 to the primitive organism, but smaller. The two new 

 organic units do not, however, behave in the same 

 way. That which retains the nucleus possesses the 

 faculty of regeneration, and of living as the primitive 

 being lived. The protoplasmic fragment, which does 

 not contain the nucleus, cannot rebuild this absent 

 organ; and though it has functional activity in most 

 respects, just as the nucleated fragment, yet it is 

 distinguished from it in others of great importance. 

 The anucleated fragment of an infusorian behaves as 

 the nucleated, and as the whole animal so far as the 

 movements of the bod^, the cilia, prehension of food. 



