294 



ARACHNOIDEA. 



CASE 

 XV. 



The most apparent difference between the male and the 

 female is, the smaller size of the former, and the different forma- 

 tion of the two posterior pairs of legs. In the male, the third 

 pair are terminated by a long bristle, and the fourth by a pedi- 

 culated sucker, whereas, in the female, both third and fourth pairs 

 are terminated by a long bristle. On the under side of the male, 

 moreover, there is a complicated series of chitonous bands, which 

 are not present in the female. When newly hatched, the young 

 Sarcoptes has only three pairs of feet, and the hind pair terminates 

 in a long bristle 3 the complicated chitonous bands have not yet 

 appeared. 



Burrow of itch mite in human skin with mite at further end. Copied trom Furstenberg. 



The insect lives in the human skin in little tunnels eaten 

 away by itself. The female, as she works her way, lays her eggs 

 behind her, as may be seen in the accompanying illustration, 

 copied from Furstenberg's work on Itch Mites. We do not know 

 how many she can lay, nor do we well see how that could be 

 ascertained \ but it is said that she lays some every day, and that 

 she may lay as many as fifty. Neither do we see how it can be 

 found out how long they take to hatch, but again it is said, from 

 seventy hours to six days. If Furstenberg's illustration may be 

 depended on, which shows a considerable number of empty egg- 

 shells dropped irregularly all along the burrow, and only one 

 unhatched close to the mite, we should imagine that the shorter 

 period was the most probable. 



The mite changes its skin four times before it attains 



