G. H. F. Nuttall, W. F. Cooper and L. E. Robinson 171 
depressions into which numerous minute pores open, hence termed the 
porose areas (p.a.); these structures will receive more detailed considera¬ 
tion later, under the heading of organs of the senses. With the 
exception of two small patches on the ventral surface, beset with minute 
stumpy hairs, the basis capituli is glabrous. 
The chitinous integument of the basis capituli is thick and strong, 
and is thickened in internal ridges which give the whole structure 
stiffness and serve for the attachment of the muscles which bring about 
the movements of the capitular appendages and the pharynx. 
The hypostome (h.), already referred to, is spatulate in outline and 
consists of a small proximal portion, whose ventral surface is smooth and 
convex, and a larger distal portion provided on its ventral surface with 
ten longitudinal files of pointed denticles which overlap one another 
from before backwards, in the manner of roof-tiles. It is divided along 
the median line by a fissure, separating the denticles into two series of 
five files, each file consisting of about twelve denticles. Although the 
number and arrangement of these denticles are fairly constant, a certain 
amount of irregularity frequently prevails, especially at the distal and 
proximal extremities. The denticles differ in size, the anterior and 
posterior being the smallest and the lateral being the largest. At the 
free extremity of the hypostome, is a thin plate of chitin continuous 
with the body of the hypostome, variable in size and studded with 
minute irregularly arranged denticles; this structure, the corona (c.), 
appears to be relatively larger in the immature stages. The upper 
surface of the hypostome is concave in a longitudinal direction and 
convex transversely; running down the median line is a small gutter (see 
transverse sections Plate XVI, Figs. 1—5), which, when opposed to the 
sheaths of the chelicerae above, forms a tube leading back to the buccal 
cavity. A longitudinal ridge runs along the lateral part of the ventral 
surface of each cheliceral sheath and a pair of slight ridges on the dorsal 
surface of the hypostome fit within the former, thus effecting a complete 
lateral closure of the space between the hypostome and chelicerae 
during the action of sucking (Plate XVI, Figs. 2, 3). 
The chelicerae (Plate XV, Fig. 4 and Text Figs. 7—-9) consist of 
a pair of more or less cylindrical appendages situated above the 
mouth. Each consists of a stout external sheath (sh.) already described 
as an anterior prolongation of the basis capituli, within which the 
chelicera proper lies, and is capable of complete retraction and of a 
considerable amount of protrusion: the two external sheaths lie in 
contact with one another throughout their length. The chelicera 
