490 PENTASTOMIDA CHAP. 
line, lies the mouth, elevated on an oral papilla, and on each side 
of the mouth are a pair of hooks whose bases are sunk in pits. 
The hooks can be protruded from the pits, and serve as organs 
of attachment. Their shape has 
some systematic value. 
There are a pair of peculiar 
papillae which bear the openings 
of the “ hook-glands,” lying just 
in front of the pairs of hooks, 
and other smaller papillae are 
arranged in pairs on the cephalo- 
thorax and anterior annul. The 
entire body is covered by a cuticle 
which is tucked in at the several 
orifices. This is secreted by a 
continuous layer of ectoderm cells. 
Some of these subeuticular cells are 
ageregated together to form very 
definite glands opening through 
the cuticle by pores which have 
somewhat unfortunately received 
the name of stigmata. Spencer 
attributes to these glands a general 
excretory function. There is, how- 
wr ever, a very special pair of glands, 
Fic. 256. — Porocephalus annulatus, the hook- glands, which extend 
ae so Ose EO ea almost from one end to the other 
; B, ventral view of animal, x 2. 
of the body; anteriorly these two 
lateral glands unite and form the head-gland (Fig. 257). From 
this on each side three ducts pass, one of which opens to 
the surface on the primary papilla; the other two ducts open 
at the base of the two hooks which lie on each side of the mouth. 
Leuckart has suggested that these important glands secrete some 
fluid like the irritating saliva of a Mosquito which induces an 
increased flow of blood to the place where it is of use to the 
parasite. Spencer, however, regards the secretion as having, like 
the secretion of the so-called salivary cells of the Leech, a retard- 
ing action on the coagulation of the blood of the host. 
The muscles of Pentastomids are striated. There is a circular 
layer within the sub-cuticular cells, and within this a longitudinal 
