TICKS. 225 



or capitulum, or rostrum, is the part which projects anteriorly from the 

 body. This carries the piercing parts which are the single hypostome 

 and a pair of piercing chitinous structures, the chelicerae. A pair of 

 palpi consisting of segments are on either side of the biting parts. 

 Very important structures are the stigmal plates. These are striking 

 mosaic-like areas which are located just posterior to each hind leg in 

 the Ixodinae and between the third and fourth legs in the Argasinae. As 

 the greatest confusion exists as to the classification of ticks, Dr. Charles 

 W. Stiles has now in hand a system of classifying ticks according to the 

 appearance of these plates as seen under the high power of a micro- 

 scope. There is great variation in the outline and general picture of 

 these stigmal plates in the different species. The stigmal orifice, the 

 opening of the tracheal system, is in the center. The Ixodinae have 

 a scutum or shield like chitinous structure on the dorsal surface. It 

 covers almost the entire back of the tick in the male and only a small 

 portion in the female. The genital opening is toward the anterior part 

 of the ventral surface. The anus, with anterior or posterior anal 

 grooves, is near the posterior third of the venter. 



Life History of Ticks. This varies greatly according to the sub- 

 family, genus and species. The female Ornithodoros savignyi lays 

 about 140 eggs. The larva does not leave the egg, but moults inside, 

 and finally emerges as an 8-legged nymph. It lives in the dust in the 

 cracks of the native huts and comes out at night to feed on the sleeping 

 natives. As the possibility for destruction are not so great as with 

 many Ixodinae the necessity for thousands of eggs is not imperative for 

 the continuation of the species as with the Ixodinae. With some of 

 the Ixcdinae the females lay from 5000 to 20,000 eggs during several 

 days or weeks and then die. The egg is preferably deposited near 

 grass. The egg stage lasts from 2 to 6 months, when the 6-legged 

 larva emerges. Crawling up the grass a passing animal is gotten 

 upon. After feeding, the larva drops to the ground, and changes to the 

 pupal stage which has 4 pairs of legs. The pupa crawls up a blade 

 of grass and gets on a passing animal (the second one). Feeding it 

 falls to the ground where it remains 8 to 10 weeks. It moults and 

 develops into an adult tick. These males and females gain access to 

 another animal the males fecundate the females, after which the 



