54 A. E. SHTPLEY 



The anterior end of the body is usually marked off from the rest — the 

 abdomen — and is termed the céphalothorax. It bears the mouth which 

 is terminal or sub-terminal and two pairs ofchitinous hooks which are 

 more or lessprotractile. The anus is terminal at the posterior end, the 

 female génital pore is just in front of it, the maie on the ventral surface 

 at the anterior end of the abdomen (1). The sexes are distinct. Ovipa- 

 rous. The females are larger than the maies. The whole body is covered 

 by a cuticle which is pierced by a number of pores, the so-called stigmata, 

 which are the orifices of certain epidermal glands. Other glands inside 

 the body hâve ducts running to the hooks and to certain papillae on the 

 head. The nervous System consists of a ventral mass with a circum- 

 oesophageal com.misure. There are no spécial circulatory or respiratory 

 organs. The metamorphosis is complète. The embryos resemble certain 

 of the Acari. They are found encapsuled in the tissues of many Verté- 

 brales, the adult forms live for the most part in the respiratory passages 

 and chambers of the air-breathing Vertebrates. 



Witli regard to the sub-division of the family, I am inclined to 

 follow Hoyle (2), who raised the sub-genera of Leackart into 

 gênera, and added certain anatomical détails to the characters 

 given by the latter writer. Thèse hâve however been criticized by 

 both W. Stiles (3) and Lohrmann (4) and their criticism seems to be 

 just, still Leuckart's distinctions are to my mind of generic rank 

 and I hâve therefore arranged the familly under the two gênera 

 Linguatula Frôhlich (o) and Porocephalus Humboldt (6). The latter 

 name was given by Humboldt with an anatomical description and 

 figure of the animal in 1811, eightyears before Rudolphi (7) named 

 the same animal Pentastomum. 



I am fuUy conscious of the inconvenience that arises from relin- 

 quishmg well-known names which are widely used and well 

 understood and which in many cases hâve even passed into text- 



(1) The position of the génital apertures is not yet satisfactorily determined 

 for ail species. 



(2) Tr. R. Soc. Edinb., XXXII, 1884, p. 165. 



(3) Loco cit. 



(4) Arch. fur Nalurg., Jahrg. 55, I, 1889, p. 303. 



(5) Naturforscher, XXIV, 1789, p. 149. 



(6) Recueil d'observations de zoologie et anatomie comparée, I, p. 298, 

 pi. XXVI, flg. 1-4. 



(7) Synopsis Entozoorum, 1819, pp. 123 and 432. 



