G-. H. F. Nuttall 
177 
the foot is provided with a large pad, equal or nearly equal in length to 
the claws. I have examined males of the following 11 species belonging 
to this category : ricinus, rasus, schillingsi, pilosus, boliviensis, cavijialims, 
rubicimdus, minor, loricatns, angustus and holocyclus, leaving only one 
species in which the foot structure remains undetermined. In all the 
species I have named the pad is large, whereas in caledonicus, canisuga, 
hexagonus, putus and vespertilionis, the pad is small, these being species 
wherein the sexes are not recorded as occurring together upon the host. 
It is clear that the large pads on the feet are correlated with the parasitic 
habits of the males in the preceding group, their presence ensuring a 
firmer foothold for the tick when upon the hostb 
It is evident that the structure of the foot in ticks requires further 
study in relation to the habits of parasitism characterizing the various 
stages. In Ixodidae, other than Ixodes, the pads appear to be of similar 
size in both sexes, and this is to be expected for both sexes in these 
species occur upon the host. 
Ixodes caledonicus Nuttall, 1910. 
Male (Fig. 1). Body oval, dark brown, 3'2 x 2'1 mm. Scutum 
hairless, glossy, with rounded protruding scapulae, slightly constricted 
antero-laterally close behind where the marginal fold appears, the latter 
broad behind; cervical grooves distinct, straight, slightly divergent 
behind, ending near the anterior third of the scutum and followed, after 
a short interval, by two large depressions whence proceed coarsely 
punctate grooves diverging slightly and extending to near the posterior 
border; the areas between the grooves protuberant, with only very 
minute, almost invisible punctations. Venter: genital orifice between 
coxae II; pregenital plate small, broader than long, indented in front; 
median plate small, widely separated from the anal plate by the adanal 
plates intervening (as in I. vespertilionis), with two lateral longitudinal 
grooves; anal plate rounded in front, with sides curved and converging 
slightly posteriorly; adanal plates large, long, broad in front, fusing in 
the median line m front of the anus, with sides nearly parallel; all the 
plates very glossy, with few minute punctations; short, coarse hairs 
1 In the larval Argas persiciis, as has been noted elsewhere, the pads on the feet are 
large. The tick in this stage clings to the host for some days, or longer. In the nymphs 
and adults (and this appears to apply to all Argasidae) the pads are small, these stages 
being characterized by their habit of feeding rapidly. It appears to follow, also in this 
instance, that the presence of the large pad in the larva is correlated with its parasitic 
habits. 
V 
12—2 
