166 MINUTE MARVELS OF NATURE 



visitors. Of course, these are rather small, and 

 may present difficulties in observation. How- 

 ever, 1 have shown a few of these considerably 

 magnified in Fig. 109. 



Fig. 109. Parasites of the common hous -Hy 



The small size of an animal gives no sort of 

 immunity from parasitism. There are, for in- 

 stance, many minute creatures that obtain their 

 sustenance by living inside the tiny green-flies or 

 aphides which so often infest our choicest plants. 

 Thus parasites attack parasites, and the pheno- 



