352 The American Naturalist. [April, 
Anyone who has attempted to get numerical results from 
serial sections, will understand the difficulty of obtaining 
approximately correct figures. In the present case, two counts 
were made in each of three series of sections, and the mean of 
these counts was taken as an approximately correct number. 
Here are the figures: 
Eggs and egg cases, 380. 
Mites in all stages of development, 109. 
Assuming that the above figures are approximately correct, 
we can make a little calculation: Multiplying the above 
numbers by 16, gives the number for one square inch ; again 
multiplying by 144, gives the number for one square foot. 
_ The average amount of epithelial covering on an adult 
human being, is said to be about 16 square feet. To be on the 
safe side, we will say that only half of the body was covered 
with scales, therefore, multiplying our last figures by eight, 
gives the number of eggs and egg-cases and mites on the host 
at the time of greatest abundance. Here are the figures in 
round numbers: 
Egg cases and eggs, 7,000,000. 
Mites, 2,000,000. 
Since the reading of this paper, I tried to determine the proportion of eggs which 
are empty, that is, hatched. It seems that from one-half to three-fourths are empty 
shells. 
As to the number of ving mites in the shed scales. This is a difficult question. I 
am inclined to believe that only a small Proportion were alive at the time the scales 
became detached. 
Indianapolis Ind. 
