46 



ter. The markings on the under side of the head and the form of the 

 caudal end of male and female seem to differ from others, but these 

 differences are unessential for the present description. The form that 

 most nearly approaches it in general appearance is the Triehodecten 

 pUosuSj Giebel, from the horse, but the latter is a relatively larger spe- 

 cies. The species is to be found on poorly nourished young sheep in 

 places where the wool is scanty. A favorite place is between the legs 

 and body, just under the shoulder. Coarse- wooled sheep are more 

 afflicted with them. 



The life history of these pests is very simple. The adults lay their 

 eggs on the wool fibers at their base, and a glutinous material sticks 

 them there (Plate V, Fig. G). The eggs hatch out in the wool, and the 

 young louse emerges by pushing off the cap (Figs. 7 and 3). The young 

 then grow to be adult. It is most probable that sheep can only get the 

 lice from other sheep, as another host of Trichodecfes sphwrocejjhaJus is 

 yet unknown. The presence of these parasites may easily be learned 

 by searching for them or their eggs. Sheep affected manifest their 

 presence by scratching themselves with their hiud feet or by rubbing 

 against stationary objects. 



Disease. — The injury wrought by this j^arasite is caused by its life- 

 habits. The injury effected by species of Trichodectes is not as de- 

 cided as that caused by those of Hwmato2)imts, the genus to which the 

 true lice belong. The mouth j)arts of the latter are so arranged that it 

 can live on the blood of its host, and iu biting through the skin it 

 causes an itching sensation and a wound. The Trichodectes, however, 

 are not fitted for penetrating so deeply, and appear to go but little 

 deeper than the epithelium. They can i^robably bite through to the 

 young growing tissue, for animals which are severely afflicted with 

 these pests have a roughened, scabby skin, which would not be the case 

 if the parasite only lived on the hairs and epithelial debris. The pres- 

 ence of these parasites on the skin not only gives discomfort to the sheep, 

 but causes the skin to thicken, become rough and covered with little 

 dry, black scabs, and the wool to become short, dry, gnarly and worth- 

 less wherever the pests attack the skin, 



