CUTICULAR TISSUE. 193 
pulled with needles in the direction of its depth, it 
stretches to eight or ten times its previous diameter, 
the clear intervals between the dark bands becoming 
proportionally enlarged, especially in the middle of the 
slice, while the dark bands themselves become apparently 
thinner, and more sharply defined. The dark bands 
may then be readily drawn to a distance of as much as 
1-300th of an inch from one another; but if the slice is 
stretched further, it splits along, or close to, one of the 
dark lines. The whole of the cuticular layer is stained 
by such colouring matters as hematoxylin; and, as the 
dark bands become more deeply coloured than the inter- 
mediate transparent substance, the transverse stratifi- 
cation is made very manifest by this treatment. 
Examined with a high magnifying power, the trans- 
parent substance is seen to be traversed by close-set, 
faint, vertical lines, while the dark bands are shown to 
be produced by the cut edges of delicate laminez, having 
a finely striated appearance, as if they were composed 
of delicate parallel wavy fibrille. 
In the calcified parts of the exoskeleton a thin, tough, 
wrinkled epiostracum (fig. 56, B, a), and, subjacent to 
this, a number of alternately lighter and darker strata 
are similarly discernible: though all but the innermost 
lamin are hardened by a deposit of calcareous salts, 
which are generally evenly diffused, but sometimes take 
the shape of rounded masses with irregular contours. 
Immediately beneath the epiostracum, there is a zone 
ty 
