Henry L. Bruner 85 
the circumstances seem to demand special facilities for hastening exuvia- 
tion in the region of the head. This demand has been met by the 
development of the moulting mechanism. 
This mechanism assists in exuviation both in a physiological and in 
a mechanical way. 
1. PHYSIOLOGICAL EFFECTS.—The high blood-pressure which distends 
the capillaries, veins, and sinuses of the head, produces at the same time 
extensive movements of the lymph. In the deeper parts of the head the 
swelling blood-vessels tend to expel the lymph from the tissues and force 
it into the chanels which lead from the head. Near the skin and 
mucous membranes, on the other hand, a large part of the lymph is forced 
toward the free surfaces; it fills the subcutaneous lymph-spaces, the 
smaller spaces of the cutis and the great sinuses, like those of the eye- 
lids. From these spaces a more liberal supply of lymph invades the 
epidermis, enters the intercellular passages of the Malpighian stratum 
and penetrates still farther, by diffusion, into the more superficial strata. 
Such effects would apparently follow from the enlargement of the blood- 
vessels alone, but they are probably augmented by a more rapid transu- 
dation which increases the amount of lymph in the tissues. 
The physiological significance of these lymph movements is evident. 
A richer supply of lymph to the epidermis means a more rapid metabol- 
ism and the acceleration of the processes of growth which prepare the 
way for the mechanical stage of exuviation. Moreover, the effects are 
probably not limited to the period of high blood-pressure alone, but con- 
tinue to be felt after normal conditions are restored, perhaps until the 
moulting mechanism is again set in motion and another active change 
of the lymph is inaugurated. 
These physiological effects are naturally felt in all parts of the head. 
They are especially important in the earher stages of exuviation, but 
they also tend to hasten the moulting of belated parts after the removal 
has actually begun. 
2. MECHANICAL EFFECTS.—The moulting mechanism facilitates exu- 
viation in a mechanical way by causing enlargement of the head. In all 
the soft parts,—in the individual scale with its capillaries, and in larger 
areas covering the superficial veins and sinuses—the skin is more or 
less stretched by the swelling blood-vessels. The lymph-vessels also con- 
tribute to the development of this condition, which reaches its maximum 
in the orbital region, where the wrinkled skin is smoothed out by blood- 
pressure in the sinus orbitalis, while the eyelids themselves are swollen 
by the distension of the lymph-sinuses which they contain. As a result 
