64 
Adaptation of TicJxS 
On the structure of the hypostome in Ixodes. 
There are 18 species of Ixodes of which the males and females are 
known. About one of these {pratti, Banks) we have no information 
such as we rec[uire for this discussion. Of the 17 remaining species, 
the sexes have been found together upon the host in 13 (I (a) and ih)), 
and in 4 (II) only the females have been found upon the host: 
I (a). In six the sexes have been found in copula upon the host, 
namely, ricinus, rasus, ugandanus, schillingsi, pilosus and holiviensis. 
The hypostomes in the males of the first five species are characterised 
by prominent basal teeth; holiviensis has a well-armed hypostome. 
I {h). In seven species {cavipalpus, rubicundus, minor, loricatus, 
tenuirostris, angustus and holocyclus) both sexes have been found upon 
the host, but there is no specific mention of their having been found 
in copula. The hypostomes of the first two species possess prominent 
basal teeth ; minor, loricatus and tenuirostris possess hypostomes which 
are well armed with pointed teeth; in angustus and holocyclus the 
hypostome is only moderately armed. 
II. In four species (hexagonus, canisuga, p)utus and vespertilionis 
there is no record of the males having been found upon the host. In 
the first two the hypostome is but moderately armed, whereas in putus 
and vespertilionis it is almost unarmed. 
The structure of the male mouth-parts, therefore, bears a direct 
relation to the presence or absence of the male iqoon the host and the 
occurrence of the sexes in copula upon the host. Of the six species 
(I (a)) which have been found in copula upon the host no less than 
five possess hypostomes with prominent basal teeth. It is probable that 
some of the species placed in the following division (I (b)) will yet be 
found in copula when they have been more carefully observed. In 
Group I (a) and (b) there are 13 species enumerated in only two of which 
the hypostome may be described as moderately armed. In Group II, 
regarding which there is no record of the males having been found upon 
the host, the male hypostome is but slightly armed in two and prac¬ 
tically unarmed in two species. 
