partial regression of the salivary glands dvrring molting or from 

 granule- bearing cells in the accessory organs. The density of 

 these granules in the coxal fluid of newly molted but unfed ticks 

 is much greater than in the fluid of engorged ticks, in which the 

 granules are more widely dispersed in the greater amount of fluid, 



Spiracular Itorphology and Function 



Argasid spiracles have been described by Robinson and Davidson 

 (1913), Cunliffe (1921), Mellanby (1935) and Browning (195U). The 

 last two workers paid particular attention to the spiraciilar struc- 

 ture and function of 0. moubata . 



As described by Mellanby, the spiracle consists externally of 

 a semicircular cribiform plate inserted into a smooth macula of 

 thickened skin, with a slitlike ostium between these. The thin 

 external layer of the plate is supported by rodlike pedicles. The 

 external layer was stated to be pierced by minute pores opening 

 into the tracheal atrium, v/hich is a tube connected to the ostiiim. 

 Muscular attachments of the macula allow opening and closing of 

 the ostium. 



If it were true that the external layer is pierced by pores, 

 it woxild appear that there is no v;ay for the tampan to close off 

 the direct connection between the external air aM the internal 

 body tracheae. Since tampans show remarkable ability to withstand 

 desiccation in the laboratory and in nature. Browning (1954A) was 

 led to investigate the spiracle anew. He found that a surface 

 view of the spiraciilar plate gives the impression of being porous. 

 On examination of transverse sections these '"pores'" are shown to 

 be expaxided distal junctures of branching pillars (pedicels) 

 arising from a basal, underlying layer of sclerotized endocuticle. 

 These pillars support the very thin outer membrane, which is, 

 however, not porous but continuous. The cavity between the basal 

 cuticle and outer membrane and ramifying between the pillars is 

 continuous between the atrium and the spiracle. From surface 

 view the hard maculum can be seen between the inner curves of 

 the crescent of the spiracular plate. The macula encloses a 

 slitlike aperture, or ostium, connecting the atrium of the trachea 

 with the outside air. The argasid spiracular plate functions to 

 provide a pad against which the macula can impinge when depressed 



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