XX SYSTEMATIC AQ5 
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 
flesh-eating creature, and there after another 
ecdysis 1t becomes adult. If, however, the second 
host eseapes this fate, the larvae re-encyst them- 
selves, and then if swallowed they are said to Fra. 261.—Eneysted 
bore through the intestine of the flesh-eater, and — form of —Poro- 
so make their way to their adult abode. ee a 
Systematic.'—The Pentastomida are a group mesentery of its 
much modified by parasitism, which has so deeply ie ees 
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, 
Porocephalus, Humboldt, and Reighardia, Ward.” The first two 
were regarded by Leuckart as but sub-genera, but Railliet * and 
Hoyle* 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. 
2H. B. Ward, P. Amer. Ass. 1899, p. 254. 
3 Nouv. Dict. de méd., de chir. et Vhyg. vétérinaires, xii. 1883. 
4 Tr, R. Soc. Edinb. xxxii., 1884, p. 165. 
