286 FRANCIS A. HULST. 



These questions are all answerable to a greater or less degree 

 after a study of sections of wrigglers from the time they are two 

 thirds grown until they are ready to emerge. Degeneration 

 begins as early as the two thirds stage and is found first in certain 

 muscles of the thorax. The next are those of the head, and 

 lastly in the abdomen extending distally from the thorax in order. 

 The appearance of imaginal organs is also made in the larva, the 

 thoracic appendages and their muscles beginning to form before 

 the advent of the pupal stage. Thus in one series of sections one 

 may study the degeneration of larval muscles and the regenera- 

 tion of the imaginal ones. Destruction is not complete in the 

 abdominal segments even in late pupal life, and it is possible, 

 indeed probable that this is completed in the adult insect. 



As to the initial cause of the degeneration of the larval muscles, 

 it has been shown that authors disagree. Kowalevsky has made 

 the attacking leucocytes or blood phagocytes (haematophages) 

 directly responsible for the disintegration, claiming that they 

 surround the muscle bundle, insert pseudopods into the sarco- 

 lemma and so break their way into the substance. The fibers 

 are broken up in this manner and the fragments ingested by the 

 haematophages. Bruyne, on the other hand, while admitting 

 phagocytic leucocytosis as an important factor in the disintegra- 

 tion of muscles destined to disappear, does not find them the 

 initial cause of the phenomena. He affirms that muscles lose 

 their striations, become fragmented and that the nuclei hypertrophy 

 before there is an appearance of leucocytes. He believes the 

 cause is to be looked for in the muscles themselves, which 

 degenerate at the end of physiological activity. 



It seems indeed probable that, metamorphosis having been 

 established in a group of insects, the phenomena of degeneration, 

 or at least of atrophy, of the organs of the adaptive life, which 

 are not to serve the adult, should occur when the limits of that 

 stage of the life are reached and such organs become inactive. 

 In such a case these organs may be looked upon as foreign 

 bodies and the phagocytes performing their accustomed office, 

 set about their removal. This seems the more probable since 

 the degenerating tissue would attract leucocytes by chemotaxis. 

 This must be modified somewhat in the case of Culex, in which 



