CHAPTER XXVII 

 Appendix to Arachnida 



Order Pentastomida : Linguatula and Porocephalus 

 (Fig. 133). 



The Pentastomida, though superficially they have some 

 resemblance to parasitic worms, are usually included among 

 the Arthropoda since their muscular tissue is striated ; but 

 their life history, for Arthropoda, is unique. 



In their adult stage they are internal blood-sucking para- 

 sites of various kinds of usually carnivorous vertebrates 



Fig. 133. — Female PorocepAaZus, 



(including mammals, birds, and reptiles), and their com^ 

 monest beats are the nasal and respiratory passages. In 

 their larval stage they are encysted parasites, generally of 

 some animal that is commonly preyed upon by the species 

 in which the adult is parasitic, so that to complete their 

 development two distinct hosts are necessary. 



The body, which is flabby and unpigmented, is either 

 cylindrical or flattened, and is often either superficially ringed 

 like that of a worm, or even serially constricted, so as to give 

 a false appearance of segmentation, like that of a tapeworm. 

 There is a distinct head, with a mouth flanked by two pairs 

 of large retractile hooks. On the head also there are numer- 

 ous symmetrically arranged papillae, on which epidermal 

 glands open. Some extremely large glands, the secretion of 



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