THE WHITE BLOOD-CORPUSCLES 923 



invertebrata the wandering mesoderm cells not only remove the 

 injured tissue but apparently give rise to new connective tissues. The 

 same function was formerly assigned to the leucocytes of mammals by 

 Ziegler, and Metchnikoff still believes that after the removal of any 

 injured tissue the emigrated leucocytes undergo elongation to form 

 so-called fibroblasts, by the further division of which are produced 

 the white fibres of the connective tissues as well as the branched 

 connective-tissue cells. Most authors at the present time have come 

 to the conclusion that the work of the leucocytes is complete with the 

 removal of dead or injured tissue, and that the process of regeneration 

 is carried out by the plasma-cells of the connective tissue, which 

 enlarge, undergo division, and form the fibroblasts of the developing 

 tissue. These plasma-cells can change their position and act as phago- 

 cytes, eating up and digesting the polymorphonuclear leucocytes which 

 have prepared the way for their regenerative activity. Their amoeboid 

 power is shown by the fact that if two sterile cover-glasses be introduced 

 under the skin, new connective tissue is formed between the cover- 

 glasses, and this method has been adopted by Ziegler for the study of 

 the cellular changes involved in the new regeneration of this tissue. 



