Gr. H. F. Nuttall 
67 
fact that many species of Ixodes are only known to science in their 
female and immature stages, it would appear probable, if my theory 
holds, that this is merely due to the males not having as yet been sought 
for in the habitats of their hosts ^ 
A great many males belonging to Haemaphysalis, Dei-macentor, 
Rhipicephalus, Amhlyomma (and Aponomma) are known, these genera 
of Ixodidae being rich in species. The males of Boophilus, Hyalomma 
Rhipicentor and Margaropus, of which there are few species, are likewise 
known. In all of these genera the males are found close to the females 
and attached to the host. These genera are chiejly parasitic on animals 
with wandering habits, and the males of these genera do not exhibit 
hypostomes which are markedly dissimilar to those of the females; 
the hypostomes are well armed in both sexes. It is only in the genus 
Ixodes that we find well-marked sexual dimorphism in respect to the 
structure of the hypostome. 
1 As a further confiimation of the views expressed in this paper, I would state that we 
have recently (March, 1911) discovered a male of Ixodes hexagonus in the nest of a 
hedgehog. This is the first male we have captured, whereas we possess hundreds of 
females, nymphs and larvae found on various hosts. The rarity of the male is rendered 
evident by the fact that there is not a single specimen of a male in the Museums in 
London, Paris and Berlin. 
v 
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