138 



PARASITES OF THE DOMESTIC ANIMALS 



structure in different species; they may be circular, oval, or comma- 

 shaped. 



9. The Genital Pore is a transverse ventro-median slit, situated ante- 

 riorly between the at- 

 tachments of the first 

 three pairs of legs. 



10. The Anus is in the 

 ventro-median line, pos- 

 terior to the attachment 

 of the last pair of legs. 



11. The Anal Shields 

 are four elongate struc- 

 tures lateral to the anus. 



They are present only in males of certain genera. 



12. Legs. — There are four pairs of legs in the adult males and females 

 and in the nymphs (octopod). In the larvae there are three pairs (hex- 



FiG. 78. — Stigmal plates of ticks: 1, Margaropus 

 Ixodes; 3. Dermacentor. 



Fig. 78A. — Stigmal plate of Margaropus annulatus (photomicro- 

 graph of mounted specimen, by Hoedt). 



apod). The pairs are numbered I to IV from before to behind. They 

 are composed of six articles or segments which are united by articul- 

 ations. 



13. The Coxa or first article is an immovable portion which lies flat 

 upon the body and upon which the first movable article is articulated. 



