90 Beport of the Billiarzia Mission in Egypt, 1915 



are absorbed and entirely disappear after the final host has been 

 reached. There are, then, in every cercaria " adult" characters and 

 " larval " characters, the former being chiefly exhibited by the diges- 

 tive, excretory and genital systems and by the oral and ventral 

 suckers, the latter by the tail and by the armature of the skin, the 

 mouth, and body. By utilizing the " adult " characters, especially 

 those exhibited by the oral and ventral suckers, the cercariae may be 

 placed in one or other of the four great groups into which the adult 

 digenetic trematodes are subdivided, namely, Gasterostomidae, 

 Monostoraidae, Amphistomidce and Distomidae. (With the exception 

 of a small group in which the body shows practically no internal 

 differentiation and to which the special name" lophocerca"has been 

 given.) For the purposes of differential diagnosis the cercariae, 

 being all at the same stage in development, may be regarded 

 tentatively as a separate group of animals, and their differentia- 

 tion based upon their most striking characters, whether they be 

 "adult" or "larval."- Tbe classification of the cercariae proposed 

 by Liihe in 1909 resolves the distome cercariae into easily recog- 

 nizable subdivisions with a corresponding descriptive terminology 

 derived partly from the generic nomenclature proposed by Diesing 

 in 1858. These subdivisions are based upon the character of the 

 tail. 



LUHE'S CLASSIFICATION. 



A. Gasterostome cercari?p. Mouth opening in tbe middle of the ventral 



surface. Intestine simple sac-shaped. Two 

 long projections from tlae end of the body. 



B. MoNOSTOME cercariae. Ventral sucker lacking. 



C. Amphistome cercarise. Ventral sucker at the posterior end of the 



bod)'. 



D. LoPHOCERCARi^. Cercaripe with longitudinal cuticular projec- 



tions along the sides of tbe body. Tail forked. 



E. Distome cercarire. Ventral sucker towards middle of body. 



(1) Cystocercous cercariiie Base of the tail forms a space into which the 



body can be drawn. 



(2) Rhopalocercous cereariiip. Tail having as great or greater width than 



tbe body. 

 (.3) Leptocercous cercarise. Tail straight, slender, and narrower than 



the body. 



(a) Gymnocepbalous cercarire. Anterior end rounded, without stylet or 



boring spine. 



(b) Echinostome cercarine. Anterior end with a collar and crown of 



thorns. 



(c) Xiphidiocercariffi. Anterior end with stylet. 



(4) Trichocercous cercaria?. Tail set with spines. 



(5) Cercariae. Tail entirely undeveloped. 



(6) RattenkonigcercarifE. Cercariae with -tails joined, forming a sort of 



colony. 



(7) Microcercous cercariae. Tail stumpy. 



(8) Purcocercous cercariae. Tail forked at its end. 



