SYSTEMATIC 495 



escape, and begins wandering through the tissues, aided by its 

 hooks and annulations, a proceeding not unaccompanied by danger 

 to its host. Should the latter be eaten by some carnivorous 

 animal, the larva makes its way into the nasal 

 cavities or sinuses, or into the lungs of the ^^B^. 



flesh -eating creature, and there after another 

 ecdysis it becomes adult. If, however, the second 

 host escapes this fate, the larvae re-encyst them- 

 selves, and then if swallowed they are said to T 



J FIG. 261. Encysted 



bore through the intestine of the flesh-eater, and form of Poro- 



so make their way to their adult abode. cepkah'* protdi*, 



. * x 1, lying in the 



Systematic. The Pentastomida are a group mesentery of its 

 much modified by parasitism, which has so deeply Hovie ) 

 moulded their structure as to obscure to a great 

 extent their origin and affinities. The larva, with its clawed 

 limbs, recalls the Tardigrades and certain Mites, e.g. Phytoptus, 

 where only two pairs of limbs persist, and where the abdomen 

 is elongated and forms a large proportion of the body. The 

 resemblances to a single and somewhat aberrant genus must 

 not, however, be pressed too far. The striated muscles, the 

 ring -like nature of the reproductive organs and their ducts, 

 perhaps even the disproportion both in size and number of 

 the females to the males, are also characters common to many 

 Arachnids. 



The Pentastomida include three genera, Linguatula, Frohlich, 

 Porocephahis, Humboldt, and Eeigliardia, Ward. 2 The first two 

 were regarded by Leuckart as but sub-genera, but Eailliet 3 and 

 Hoyle 4 have raised them to the rank of genera. They are 

 characterised as follows : 



Linguatula, body flattened, but dorsal surface arched ; the edges 

 of the fluke-like body crenelated ; the body-cavity extends as 

 diverticula into the edges of the body. 



Porocephalus, body cylindrical, with no diverticula of the body- 

 cavity. 



Reighardia, devoid of annulations, transparent, with poorly 

 developed hooks and a mouth-armature. 



1 Shipley, Arch, parasit. i. ( 1898, p. 52. This contains lists of synonyms and 

 of memoirs published since Stiles' paper, etc. 



2 H. B. AVard, P. Amer. Ass. 1899, p. 254. 



3 Nouv. Diet, de mtd., de cfiir. et d'hyg. vtterinaires, xii. 1883. 



4 Tr. R. Soc. Edinb. xxxii., 1884, p. 165. 



