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The family Koellikeriadae (Didymozoidae Mont.). 



By 



G. A. MacCallum, M. D. and W. G. MacCallum M. D. 



(From the Department of Pathology, Columbia University, New York.) 



With Plate 13. 



The genus Didymo^oon was created by Taschenberg, 1878, 1879 

 to comprise "worms elongated, sometimes kidney sliaped or grown 

 together in a ring with demarcated, often thread-like neck ; without 

 suckers. Pharynx spherical or oval, intestine present or absent. 

 Testes forming a tube in numerous convolutions. Egg bearing canal 

 extending in coils with the latter throughout the body. Genital 

 orifice at the anterior body end. Vitellarium absent. The small oval 

 eggs with chitinous shell present in millions in the Uterus." The 

 genus Nematohothrium later ranged with Dkhjmosoon in this family 

 by MoKTiCELLi and Braun is not concisely deflned by van Beneden. 

 Braun describes them as vcry much elongated Didymozoidae without 

 intestine but with mouth opening and with genital pore at the 

 head end. 



These two genera make up the family Didymozoidae (Monticelli, 

 1888) defined by Braun as follows: Digenetic trematodes living 

 always in pairs in cysts without Separation of sexes. Anterior part 

 of body narrowed into a neck, posterior part cylindrical or swollen 

 into kidney shape; sometimes two individuals are grown together. 

 Mouth sucker alone present ; pharynx rudimentary or absent ; intestine 

 present or absent. Genital pore in front of mouth, terminal. Testis 



Zool. Jahrb. XXXIX. Abt. f. Syst. 10 



