TONGUE WORMS : EXTERNAL ANATOMY 699 



species have been recorded from man by Welch, Osier, and Flint. It 

 is not clear, however, as to whether the invasion of the human body by 

 tongue worms actually results in a disease condition, somewhat loosely 

 spoken of as Porocephaliasis ; the parasites have never been recorded 

 in large numbers and it would appear that the few which have been 

 found represent an accidental infection, and that man is not the true 

 host of any of the species. 



In 1907 the senior author, while studying the haemogregarines of 

 snakes, noted the occurrence of encysted gregarine-like parasites in the 

 salivary glands of Porocephalus pattoni ; these have since been described 

 by Prowazek, who regards them as the developmental stages of the 

 blood parasites of the snakes ; there is at present no proof that this is 

 the case. 



EXTERNAL ANATOMY 



The adult linguatulid is vermiform in shape and of a white colour ; 

 it may be cylindrical throughout, or the ventral surface may be flat and 



the dorsal rounded. The anterior end that by which it 



. . General structure 



fixes itself to its host is broad and rounded, and the 



posterior extremity is attenuated. The cephalothorax the rounded 

 anterior portion merges into the body, which forms the largest part of 

 the animal. The integument may be divided up into annuli or segments, 

 and is pierced by numerous minute pores which are the orifices of 

 dermal glands. Legs are wanting. 



The mouth is situated on the ventral surface of the cephalothorax and 

 is usually subterminal, but may be terminal ; it lies in the middle line 



and is oval in shape, and is surrounded by a well devel- 



Mouth parts 



oped chitmous framework (Plate LXXXVIII, fig. 4). 

 Lying on each side of it there is a pair of chitinous hooks which can 

 be retracted into grooves ; in the living condition they are retracted 

 and protracted like the claws of a cat, and it is evident that the animal 

 uses them not only for fixing itself to the tissues of its host, but for 

 puncturing the membrane in order to draw blood, for the adult linguatulid 

 is a blood-sucker. 



The sexes are distinct, and the male is always smaller than the "female ; 

 the genital opening of the latter is situated at the posterior end of the 

 body just in front of the anus; in the male it is situated high up near 

 the junction of the cephalothorax with the abdomen. 



The most valuable taxonomic characters are the number of annuli, the 

 shape of the cephalothorax and the structure of the hooks. 



