SEVENTEENTH ANNUAL REPORT. 



387 



this artif cial table, it should, of course, be verified oy means of the 

 illustrations, the more detailed keys, or the descriptions. 



It may here be mentioned that the common sheep tick was formerly 

 supposed to be closely related to the cattle ticks and dog ticks, and in 

 the writings of pre-Linnaean authors the terms lice, ticks, Reduvms^ 

 and Ricinus cover much more than they do to-day. Even Linnaeus as 

 late as 1761 mentions the sheep tick {Melo2)hagus ovmus) as an acarine 

 {Acarus reduvius). Gradually, however, by the process of elimina- 

 tion, the sheep tick has been placed where it belongs — in the insects — 

 but it has still retained its old vernacular name which it has had for 

 several centuries. 



THE GENERAL STRUCTURE OF TICKS. 



In order properly to determine a tick it is necessary to become 

 acquainted with the general anatomical parts, particularly with the 

 external anatomy, and to understand the technical 

 terms used. Unfortunately there is considerable con- 

 fusion in regard to the terminology as adopted by 

 various authors. This is largely due to attempts to 

 homologize the various structures of the tick with 

 corresponding structures of the insects. The termi- 

 nology used in this paper may be seen from figs. 43 

 to 68. 



The ticks are air-breathing arachnoids, which are FiG.47.-Dorsaiviewof 



1 1 1x1 -.1 ii 1 1 nymph of Boophilus 



always large enough to be seen with the naked eye; annuiatus of North 

 young specimens just born are very small, but still it^e^^'orjrnlr''' 

 visible without the aid of a microscope; fully replete 

 forms may be over half an inch in length. Several different forms are 

 recognized in each species, as given below: 



Adult or replete females (figs. 43, 44), which have eight legs. 



Adult males (figs. 45, 46), also with eight legs, usually somewhat 

 smaller and flatter than the females. 



Nymphs (fig. 47), which are half -grown eight- legged females. 



LarvcB (figs. 48, 49), which are six-legged and without sexual orifice. 



Eggs (fig. 50), which have a rather hard, leathery shell. 



Young specimens and males are rather flat; females become rounded 

 and plump with increasing age. 



Upon even a superficial examination it will be noticed that ticks are 

 composed of two more or less distinct portions united by an articula- 

 tion. These parts are known as the capitulum, or head, and the hody. 

 By using these terms in this manner we do not intend to imply that 

 all of the parts of the head of the insects are contained in the capitulum. 



I. Capitulum, or head.— The capitulum (figs. 52-54), also known 

 as the head or the rostrum, is the small anterior structure with the 

 mouth parts; it is attached to the anterior extremity (figs. 45, 46) in 



