396 



BUREAU OF ANIMAL INDtTSTKl. 



(3) The anal shields^ or plates (clypei), (fig. 62) are present only in 



the male of certain genera. They are 

 elongate in form, four in number, and 

 are lateral of the anus. Certain forms 

 {Ixodes) also have other ventral shields. 



(4) The stigmata (stigmal plates, or 

 peritr ernes) are two in number (fig. 62), 

 lateral or slightly ventral, one on each 

 side of the body. In the Argasidse 

 they are between the III and IV pairs 

 of legs; in the octopod stages of the 

 Ixodidse they are back of the IV pair 

 of legs. It is usually stated that they 

 are not present in the hexapod stage, 

 but in certain forms (as in Boophilus 

 annulatus) they are present (fig. 62), 

 being situated between coxae II and 

 III. We have frequently found larval 

 ticks which presented three pairs of 

 stigma-like structures: One pair be- 

 tween coxae I and II; a second pair 

 between coxae II and III; and a third 

 pair, which appears to be either double 

 or to be close to an unusuall}^ promi- 

 nent chitinous ring, posterior to coxae 

 III. 



The stigmal plates vary in form and 

 structure in the different species and 

 are important systematic characters. 

 We may recognize the entire struc- 

 ture as the stigmal plate^ or peritreme, 

 with a stigmal surface^ with an open- 

 ing known as the stigmal aperture, or 

 spiracle. 



(5) Furrows and grooves. — Various 

 furrows or grooves (fig. 62) may be rec- 

 ognized on the ventral surface. The 

 most important of these are a pair of 

 genital furrmm and the anal fnrroiv. 

 The former extend, one on each side of 

 the median line, from the region of the 

 genital pore backward, diverging back 

 of coxae IV, and ending near the pos- 

 tero-lateral margins. 



(6) Pits, pores, punctations, hairs^ 



Fig. 67. — Tarsus II of spinose nymph 

 of Ornithodoros Megnini. Greatly en- 

 larged. Original. 



and spines. — (See p. 395, under "Dorsal structures.") 



