THE ACARIIN^A OR MITES. 



129 



copiilatory suckers near the tip. There are frequently sexual differences. Some ntales 

 have the third pair of legs very large and long, while the fourth pair is very small. 

 Sometimes there are platelike lobes at the tip of the male abdomen, and the tarsi 

 may terminate differently in the two sexes. The 

 Sarcoptidae live in the skin of mammals, includ- 

 ing man, and a few species of birds. The female 

 IjiuTowsinto the skin, depositing eggs on the way. 

 The young, on hatching, start bvurows of their 

 own, so that a host is infested in patches. These 

 burrows or cuniculi are close to the sml'ace, and 

 sometimes result in loosening pieces of the epi- 

 dermis so as to produce a scaly effect or crust. 

 Frequently there are vesicles, palpules, or pus- 

 tules, which may become ulcerated by scratch- 

 ing. The different species produce different 

 effects, and even the same species when on dif- 

 ferent animals. When upon a hairy animal, the 

 hair usually falls out in the affected portion. 



The young Sarcoptes, when newly hatched, has 

 but three pairs of legs; the last ending in a long 

 bristle; and there are no chitinous bands. Some 

 species molt four times before maturity. \\Tien 

 adult they pair, and the female wanders a little 

 in search of a good burrowing place. At this time 

 the mites can exist for a long period if removed from their hosts and kept in a moist 

 situation; but if exposed to dryness they soon die. The burrow is made by eating the 

 tissue, and is of the size of the mite. As the female (fig. 267) progresses she leaves 

 behind her a row of from 10 to 40 large eggs and a considerable amount of "frass." 

 The female, having deposited her complement of eggs, dies at the end of her burrow. 



Fig. 266.— Leg of a Sarcopte 

 illustration. 



(Author's 



Fig. 2&7.— Sarcoptes in her burrow, and eggs. (Author's illustration.) 



As the skin of the host is always wearing off and constantly being renewed from below, 

 the eggs, when ready to hatch, will be close to the surface, so that the mites may 

 readily escape. Above each burrow there is often a little pimple, containing a watery 

 fluid. There appears to be no means of distribution from individual to individual 

 except by contact. Many of the species that are normally confined to one host can 

 live on other animals and on man. The eggs If kept moist may retain their vitality 

 for a week. 



