50 



PARASITOLOGY. 



are provided with ambulacrum and the third pair with 

 one bristle at each terminal extremity. 



Female. — The first two pair are provided with am- 

 bulacrum and the last two pair with one bristle at 

 each terminal extremity. 



The genus Psoroptes, species Communis, is pro- 

 vided with a head that is longer than broad ; the 

 rostrum is conical in shape and elongated, and not 

 margined by cheeks. 



Male. — The first three pair of legs are provided 

 with ambulacrum, the fourth pair with two bristles. 



Female. — The first two and fourth pair of legs are 

 provided with ambulacrum. The third pair with two 

 long bristles. 



The genus Symbiotes, species Communis and 

 Auricularum, — rostrum as wide as long, and desti- 

 tute of cheeks. 



Male. — All legs are provided with ambulacrum. 



Female. — The first, second and fourth pair are 

 provided with ambulacrum and the third pair with 

 two bristles. 



LIFE HISTORY OF THE FAMILY SARCOPTIDAE. 



The life history is divided into five stages, viz.: 

 The oval, larval, pupal, adult and ovigerous female. 



First Stage. — Ova. — Under favorable conditions the 

 eggs hatch in five to ten days. 



Second Stage. — Larval Stage. — Six-legged and asex- 

 ual ; it passes through two or three moults. 



Third Stage. Nympha. — The last moulting in the 

 larval stage adds a fourth pair of. legs ; no sexual 

 organs ; the males and females are distinguished by 

 the difference in size, the females being larger. 



