NATURAL HISTORY. 17 
its head sideways this intermediate link enfolds 
itself within the first segment, without disturb- 
ing its position. The skin of this animal is 
covered with a series of longitudinal stripes or 
cords, as shewn in the engraving. From this 
structure it happens, that, when the larva twists 
or turns part of its body, the segments in those 
places become less transparent, the longitudinal 
lines assuming a spiral direction, and present- 
ing the appearance of a many-threaded screw, 
while the under and upper ones, crossing each 
other, stop a portion of the light. On reas- 
suming its straight position, its transparency is 
instantly restored. These alternately opaque 
and pellucid appearances seem, at first glance, 
to arise from a power in the creature to change 
its colour, but explained as above, which may 
be verified by means of a strong magnifier: the 
mystery vanishes, and we see how admirably 
Nature has adapted its structure for the pur- 
poses intended; for, were it not for these longi- 
tudinal cords, in turning or twisting, a con- 
siderable pressure, and consequent injury, would 
have been sustained by its internal parts. 
The head is furnished with two pair of eyes; 
the anterior ones, which are situated near the 
mouth, are smaller than the others. Two large 
