OF WASHINGTON. 283 



know, however, that the great, the moving instinct of this animal, 

 even in the newly-hatched, minute larva, is to fasten itself to a 

 vertebrate animal. It prefers a mammal, on which it selects a 

 spot where the skin is soft, and then introduces its sucking appara 

 tus into the epidermis. The larva, of course, cannot penetrate 

 deeply enough into the skin of the host to draw blood ; but the 

 irritation of the sting causes a suppuration, on which the young 

 larva feeds. When, however, blood is struck, the little flat, semi- 

 transparent creature soon becomes distended, the body rounded, 

 and the color dark red. This state of life, stimulated by the 

 nourishing food, hastens the process of development, and in a week 

 the larva is transformed into the nymph, which at the expiration 

 of another week is changed into the mature individual. Although 

 the male lives upon the host and, like the female, fastens itself upon 

 the skin, it has never been observed to suck blood ; consequently 

 its form and size remain unchanged and it presents the same 

 flattened shape which it has in the free-living state. 



Thef act that its whole body is covered on the dorsal surface by 

 a hard chitinous shield shows that it is unable to expand, and 

 proves that it is not destined by nature to get nourishment from 

 blood like the female. The male Tick seems to be tempted to 

 dwell on the host only to be in company with the female. 



It fastens itself by the rostrum, with a view of procuring a se 

 cure position under the female, so that the act of copulation may 

 be carried on without disturbance. In examining the female 

 while feeding upon a mammal or bird we find the body im 

 mensely distended. Pagenstecher states that the length of a full 

 female has increased 925 per cent, for it has increased from 2.75 

 mm. to i cm. ; its width shows an increase of 200 per cent., 

 while the increase of the height is much greater, as the dorsum 

 formerly nearly touched the ventral tegument ; the body is now 

 5 mm. high. But this expansion is not equally represented on 

 all parts of the body. The shield preserves the same size and in 

 proportion to the body now appears very small. 



One other part of the body also retains its former size. This 

 is the short region between the insertion of the capitulum and the 

 sexual opening ; for during the process of egg-laying the capitu 

 lum retracts and each egg passes over it to the pedicel (by which 

 the capitulum is connected with the body), where the egg receives 





