152 WITHROW MORSE. 



HlSTOLOGICAL ' EVIDENCE. 



In the accompanying photomicrographs, evidence is presented 

 that events have occurred in the tail of a larva before the advent 

 of phagocytosis. Fig. I is that of a section through the larval 



FIG. i. Section through the tail of an involuting Rana pipiens. Zeiss 2 mm. 

 obj. ocular 6. Osmium tetroxid fixation. Heidenhain's ferric alum-hematoxlyn. 



frog's tail, lateral and ventral to the nerve and vertebral column. 

 The frog was without any external indications of the approaching 

 metamorphosis. However, the section shows that the process is 

 under way, for there is a dissolution of the muscle bands, a loosen- 

 ing up of the fibers, and, in the larger spaces, phagocytes are to be 

 seen in the act of engulfing portions of the dissociated muscula- 

 ture. The important point to be noted, however, is that there 

 has been a change in the condition of the musculature in regions 

 where no phagocytes occur. This change involves what has 



