L. E. Robinson and J. Davidson 
245 
appendages and pharyngeal muscles receive their blood supply from 
the same source. The blood finds its way back to the heart through 
the lacunar spaces between the organs of the body. The coelomic space 
immediately round the heart may be looked upon as a pericardial sinus, 
though no enclosing membrane, comparable with that of the above- 
described sinuses, can be identified. Active circulation of the blood is 
brought about in the middle and hinder parts of the body by the con¬ 
tractions of the dorso-venti’al body-muscles. 
The blood of the tick is a colourless fluid, consisting of a clear 
plasma in which are suspended' large nucleated amoeboid corpuscles 
(see PI. XVII, fig. 2, hi. cp.) which are sufficiently numerous to make 
a drop of blood such as issues from a puncture in the body-wall of the 
living animal appear distinctly turbid. 
The respiratory system. 
Part I, Plate III, fig. 6; Part II, Plates XIV and XVI. 
Text-figures 6 and 7. 
The respiratory organs of A. persicus resemble those of the Ixodidae, 
in that they consist of a pair of spiracles and a highly developed system 
of tracheal tubules. 
The literature on the subject having been reviewed in detail by 
Nordenskibldh Bonnet^ and Samson®, it is unnecessary in this paper to 
repeat their remarks. 
The position and external appearance of the spiracles received con¬ 
sideration in connection with the anatomy of the external parts of this 
tick (see Part I, pp. 32-33). 
In 1908, Nuttall, Cooper and one of the present authors (L. E. R.) 
made a special study of the spiracle of an Ixodid tick (Haemaphysalis 
punctatay, and a comparison of the structures then described, with the 
corresponding parts of the spiracle of A. persicus, makes an interesting 
study ; but before making such a comparison, it would, perhaps, be 
better to proceed first with a description of the internal structui’e of the 
spiracle of the latter species. 
Externally, the spiracle appears as a small, nearly circular, salient 
boss which protrudes from the ventral body-wall. Its surface is divided 
1 Nordenskiold, E. (1909), p. 4-56. ^ Bonnet, A. (1907), pp. 44—50. 
® Samson, K. (1909 a), pp. 205-209. 
Nuttall, G. H. F., Cooper, W. F., and Robinson, L. E. (xii. 1908). 
