276 
Annual Report for* 1906 of the Zoologist. 
because of their comparatively large size, for mites, as a rule, 
are extremely minute animals. They are not insects, but 
Arachnids — a class which includes the spiders and scorpions. 
When fully grown they have eight legs, but on the way to 
maturity from the egg they pass through two stages. From 
the egg a six-legged “larva” hatches out, and this in turn 
develops into a “nymph,” which is eight-legged, but differs 
in important respects from the 
adult, especially in being sexu- 
ally immature. 
The female tick can distend 
itself to a ridiculous extent by 
sucking the blood of its “host,”' 
and it is not unusual to attain 
a length of fully an inch, with 
a proportionate breadth and 
thickness ; though the unfed 
animal may be considerably 
less than a quarter of an inch 
Fig. 4.— Male of Dermacentor reticulatus long and as flat as a bug. This 
from below, x io. distention makes all female 
ticks look much alike to the inexperienced eye, and to dis- 
tinguish them the mouth parts, legs and other structures not 
affected by distention have to be carefully studied. The male 
tick, on the other hand, is almost entirely covered by an 
inelastic “scutum” or shield, which prevents it from swelling 
to any considerable extent, and it is therefore more easily 
recognised. 
The ordinary life-history of a tick is extremely eventful, 
being spent partly on the “host” and partly on the ground. 
When gorged, the female drops to the ground, having been 
previously fertilised by the male while attached to the cow, 
sheep, or other animal on which it is parasitic. 
It seeks out a recess in the soil, and proceeds 
to lay a prodigious number of eggs, sometimes 
amounting to several thousand, occupying 
several days in the process. Each egg hatches 
out, after a period which may extend over 
days or months according to the temperature, 
into a tiny six-legged larva, whose further 
development entirely depends on its success 
itself to some passing animal. It may have to wait, fasting, 
for weeks or months before such good fortune befalls it, and 
no doubt a large proportion of the larvsn perish without 
attaining their object. During the waiting period they climb 
about among the herbage, showing great excitement and 
activity as any animal approaches, and seizing instantly upon 
Fig 5.— Larva of 
Ixodes ricinus. 
m 
attaching 
