48 THE LIFE-STORY OF INSISTS [CH. 



adapted to the altered body-form of pupa and 

 imago. 



The destruction of larval tissue and the develop- 

 ment of replacing organs from special groups of cells, 

 derived of course from the embryo, and carrying on 

 the continuity of cell-lineage to the adult, are ainoni; 

 the most remarkable facts connected with the life- 

 story of insects. The process of tissue-destruction 

 is known as 'histolysis'; the rebuilding process is 

 called t histogenesis.' Considerable difference of 

 opinion has existed as to factors causing histolysis, 

 and for a summary of the conflicting or comple- 

 mentary theories, the reader is referred to the work 

 of L. F. Henneguy (1904, pp. 677-684). In the histo- 

 lysis of the two-winged flies, wandering amoeboid 

 cells like the white corpuscles or leucocytes of 

 vertebrate blood have been observed destroying 

 the larval tissues that need to be broken down, as 

 they destroy invading micro-organisms in the body. 

 But students of the internal changes that accompany 

 transformation in insects of other orders have often 

 been unable to observe such devouring activity of 

 these 'phagocytes,' and attribute the dissolution of 

 the larval tissues to internal chemical changes. The 

 fact that in all insect transformation a part, and in 

 many a large part, of the larval organs pass over to 

 the pupa and imago, suggests that only those struc- 

 tures whose work is done are broken down through 



