THE ACAEINA OK MITES. 



61 



Fig. 113.— Egg of 

 Margaropus an- 

 nulatus. (Au- 

 thor's illustra- 

 tion.) 



radically from tliat of Europe. About 50 different kinds of ticks are now known from 

 the United States, and several others will yet be discovered in the genus Ixodes. A 

 number of these, however, are found only in the extreme southern parts of our country. 

 In most places it is possible to fmd 5 or 6 species of ticks. 



Dr. George Neumann, of Toulouse, France, is the great authority on ticks, and ho 

 has described fully half of the 400 known species. 



The internal anatomy of the Ixodidae has been examined by Heller (1848), In- 

 ! Pagenstecher (1861), and recently by Nordenskiold, Samson, and others. The 

 pharynx soon contracts into a slender oesophagus, which, as usual, 

 passes through the "brain " and into the stomach. The latter is not 

 very large, btit has several diverticula or caeca, some in front, and 

 I usually four large ones behind and a longer one on each side. The 

 I color of the food in the caeca often shows through the integument, 

 so that the same species at different times exhibits different mark- 

 ings on the body. Upon this basis the earlier authors often de- 

 scribed one species under several names. The intestine is short 

 and straight, enlarging somewhat before the anus. The breathing 

 apertures or spiracles open into a larger sac, which often di^ddes into 

 a host of small tracheae that spread out in the body cavity. In the anterior part of the 

 body there are two large, botryoidal salivary glands, opening through a duct each side 

 of the mouth. The female genital organs consist of two elongate ovaries, each with a 

 slender o\dduct, which unite shortly before the \njlva. The male organs consist of the 

 two slender testes, each emptjang into a large median sac, from which a slender duct 

 leads to the opening. In mating, the ventral siufaces are apposed; the male intro- 

 duces his mouth parts into the vulva of the female for a short time; then the aper- 

 tures are apposed and the spermatophore issues from the male and is pushed into the 



A-ulva of the female by his hypostome. A 

 secretion of the liquid from the coxal 

 glands of the male probably assists the 

 process. The male, after becoming ma- 

 ture, usually feeds before mating. 



In recent years ticks have become prom- 

 inent from the connection of certain spe- 

 cies with certain diseases, so that many 

 writers and many publications are appear- 

 ing and the family is becoming well 

 known. It has long been known to cat- 

 tle raisers in the Southern States that cat- 

 tle dying from Texas or Spanish fever 

 were infested with ticks, and it was there- 

 fore quite nattiral for them to attribute the 

 disease to the tick. Veterinarians, how- 

 ever, did not believe it, and Gamgee, in 

 his extensive report on the diseases of cattle (1869), argued against the supposed con- 

 nection. In 1880 a report on the louping-ill of sheep by a committee of the Teviotdale 

 Farmer's Club in Scotland brought out the fact that Ixodes were very abundant on all 

 afflicted animals and suggested that the ticks were in some way responsible for the dis- 

 ease. In 1890 Dr. P. Paquin considered the tick as an agent in transmission of cattle 

 fever, btit had little actual e\ddence. On the basis of "He discovers who proves" the 

 credit belongs to Kilbome and Smith. In 1889 Dr. L. Kilbome thought to test the pop- 

 ular theory and became convinced that the cattle tick was necessary in the transmission 

 of the disease. Later he, with Dr. Theobald Smith, proved that the tick was an inter- 

 mediary host of the blood parasite causing the disease, and Dr. Smith described the 

 parasite as Fyrosoma bigeminum, now Babesia. Southern cattle accustomed to tick 



Fig. 114.— Dcrmacentor variabilis: Male from 

 below. (Author's illustration.) 



I 



