490 



PENTASTOMIDA 



CHAP. 



line, lies the month, 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 annuli. The 

 entire body is covered by a cuticle 

 which is tucked in at the several 

 orij&ces. This is secreted by a 

 continuous layer of ectoderm cells. 

 Some of these subcuticular cells are 

 aggregated 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- 

 ever, a very special pair of glands, 

 the hook -glands, which extend 

 almost from one end to the other 

 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 



Fig. 256. — PorocepJialus annulatus, 

 Baird. A, Ventral view of head, x 

 6 ; B, ventral view of animal, x 2. 



