No. 2.] EPITHELIUM OF DRAGONFLY NYMPHS. 113 



be not actual replacement happening before one's eyes, it comes 

 as near it as the nature of the case will admit. 



One naturally asks what becomes of the remnants of the old 

 cells, and whether there is any connection between their dis- 

 appearance and the rapid growth of the young cells. On 

 these questions I have obtained no light. 



Summarizing their history, we may say, then, in a word, the 

 epithelial cells originate by divisions in the cells of the nidus, 

 grow, crowd their way to the surface, acquire a striated border, 

 become functional, secrete, discharge, digest, and die, and then 

 give place to others which will run the same swift course. 



