L. E. Robinson and J. Davidson 
221 
have the hypodermal layer persisting on their coelomic surfaces, though 
in places it may be so thinned-out as to become almost unrecognisable. 
A remarkable feature in Argas is the almost complete suppression of 
the dermal glands, which form such a conspicuous character of the 
hypodermis in the Ixodidae. The very few minute pores which are 
found sparsely scattered over both the dorsal and ventral surfaces of the 
body, are quite rudimentary, and the underlying hypodermis shows, at 
the most, a very vestigial gland-structure. In the case of Ixodes ricinus, 
Nordenskibld^ has observed that in old individuals, the originally 
columnar hypodermal cells become flattened, and the dermal glands 
disappear. We have noticed the same degenerative tendency in the 
hypodermis of other Ixodid ticksl In the case of Argas, however, the 
description given above applies to the young adult forms, and to the 
nymph ; concerning the hypodermis of the larva, we have no information. 
It would appear, therefore, that in Argas, the hypodermis has ful¬ 
filled its main purpose when the cuticle is formed, and that it then 
assumes a quiescent state until the arrival of the next moulting period. 
The secretory function which is so well developed in the Ixodidae 
seems to be entirely suppressed. 
As in other ticks, the cuticular layer shows an outer layer of dense 
highly-refractive chitin and an inner thicker layer of softer chitin which 
stains readily with acid dyes. The horizontal stratification which is 
so well shown in the deeper portions of the cuticle of the Ixodid 
ticks, is absent, but the delicate fibrillar canaliculi, which Nordenskibld^ 
has described and figured so beautifully in his work on I. ncinus, are 
very evident in suitably prepared sections of the cuticle. These canali¬ 
culi commence at the internal surface of the cuticle and run directly 
towards the external surface, some little distance below which they 
terminate blindly. Many follow a somewhat undulating course, but as 
far as can be seen, they do not branch or fuse with each other. We 
have not been able to assure ourselves that these cuticular canaliculi 
contain protoplasmic processes derived from the hypodermis, as 
Nordenskibld found to be the case in /. ricinus. In preparations 
stained by the ordinary methods this structure of the cuticle is very 
difficult to see, on account of the extreme transparency of the parts. 
NordenskibhR recommendsGolgi’s Silver-Chromate impregnation method 
^ Nordenskiold, E. (1908), pp. 657-658. 
^ Haemaphysalis punctata, Rhipicephalus appendiculatus and Amblyomma hehraeum. 
3 Nordenskiold, E. (1908), pp. 659-664 ; PL 26, fig. 8, and PI. 28, figs. 16-18. 
■* Nordenskiold, E. (1908), p. 660. 
