370 
Regeneration in Argas persicus 
Thus, the formative substance for the second tarsal claw, during growth 
periods, is continually passing to that part of the animal, and in the 
case of the larva the rudiments of the nymphal claw are similarly 
being deposited. These formative substances might be supposed to be 
stimulative in their action, merely directing the construction of the 
nutritive substances into the specific parts of the organism. 
We may assume that the amount of nutriment supplied to each 
part of the body is constant. Accordingly, when two articles of a leg 
are removed, during the regeneration called forth by the continued 
deposition of formative substances, food material is used up which 
ordinarily would have been available for the other articles and only 
after the missing parts have been replaced can any further growth of 
the whole limb take place. This would explain the reduction in size 
of all the articles of the leg even when only one or two distal articles 
are removed. 
The deposition of formative substances seems to cease some time 
before the animal moults, and beyond this point no regeneration can 
take place, even though plenty of food material may be available. 
In the case of the larva, the deposition of stimulative material usually 
stops before the animal has finished feeding, and as a result no re¬ 
generation takes place even when the legs are amputated immediately 
after the tick has become fully gorged and plenty of food material is 
available. In the nymphs the deposition ceases at a point about midway 
between feeding and moulting. This period we have arbitrarily referred 
to as the pre-amputation period. The extraordinarily short pre-ampu¬ 
tation period in the larva suggests that Argas persicus is gradually 
suppressing its free, active larval stage and that most of the formative 
substance of the nymphal legs is deposited before the larva hatches 
from the egg. An almost complete suppression of the free larval stage 
occurs in two other members of the Argasidae, Ornitliodorus savignyi and 
0. moubata. In the former the larva emerges from the egg and has 
some (although very slight) power of movement. In the latter species, 
however, the suppression is carried further; the majority, though not 
all, of these larvae emerge from the egg-shell, but all are without power 
of movement. Further, the larvae of both these species pass to the first 
nymphal stage without feeding. 
