L. E. Robinson and J. Davidson 
235 
elaborated from the contents of the stomach, and passed on in this form 
to the coelomic spaces surrounding the gut, to be carried to the different 
parts of the body by the blood stream. In Ixodes ricinus, Norden- 
skibld^ has actually observed that the epithelial cells of the stomach 
and its coecal appendages put forth pseudopodial protrusions from their 
basal surfaces, which ultimately rupture and discharge their elaborated 
nutrient products into the coelom. We have never seen this pheno¬ 
menon in Argas persicus, but that it does occur is probable, from the 
fact already mentioned, that during the digestive process large numbers 
of spherical granules, which appear to be identical with those contained 
within the epithelial cells, are found in the coelomic spaces. 
The foregoing description of the gastric epithelium applies to both 
the stomach and its coecal appendages; the two parts do not show any 
marked difference in structure, except that in the central stomach the 
epithelium does not show such great activity during the period of 
digestion as does that of the coecal appendages. 
An interesting point in connection with the digestive process in 
A. persicus, is that the large crystals, which appear in the ingested 
blood mass in Ixodid ticks, have never been observed. 
After digestion is completed, the gastric epithelium undergoes a 
process of degeneration; the cells become packed with dirty brownish- 
black granules of excretory matter, and the details of their original 
structure is lost. The lumen of the mid-gut still retains a mass of 
similar granules embedded in a homogeneous matrix of a paler dirty- 
brown colour. Whether the walls of the alimentary coeca and stomach 
undergo a complete histolysis and regeneration between each moult, in 
A. persicus, we cannot at present state. 
The various phases through which the tick passes in the course of 
its life, makes the study of histological detail no easy matter. As 
Nordenskiold^ observes, the transformations are very difficult to follow 
in a sequent manner, and in order to investigate the subject properly, 
it would be. necessary to carry out a lengthy and troublesome research 
with this special object in view, using material raised under such 
conditions that its history was definitely known. 
The muscular layer of the stomach wall does not appear to be so 
highly developed in A. persicus as that observed by Nordenskibld^ in 
I. ricinus. The muscle bands form an irregular interlacing network which 
extends over the entire surface of the organ, but is not differentiated 
* Nordenskiold, E. (1908), p. 645. - Nordenskiold, E. (1908), p. 643. 
^ Nordenskiold, E. (1908), pp. 671-673. 
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