144 G- A. and W. G. MacCallum, 



of the others. Anterior part of body narrow, posterior part cylin- 

 drical or swoUen into kidney shape: sometimes two individuals are 

 grown together. Siickers rudimentary or very feebly developed. 

 Both may be present or one or botli may be absent: pharynx and 

 intestine may be rudimentary or absent. Genital opeuing near 

 raoutli. Ovary and yolk gland long convoluted tubes meeting in a 

 Shell gland at beginning of a long tubulär uterus. Eggs yellow and 

 rounded. Testes saccular or tubulär witli long convoluted vas 

 deferens. No muscular cirrus. Many forms are supplied with a 

 nutritive vascular film from the liost. 



The Situation may be presented most clearly by giving a brief 

 summary of the descriptions of the forms which appear to belong in 

 each of the long accepted genera Didymosoon and Nematohothrium. 



Genus Koellikeria Cobb. {Didymosoon Taschenbeeg). 



K. (D.) thynni Taschenberg. (Monostomiim bipartitum Wedl, 

 Wagener etc.) 



Wedl's description follows: Cysts 3 — 4 mm in size found on the 

 gills of Tlnjnnus vulgaris contain one or two peculiar monostomes. 

 There is a pyriform head and reniform body connected by a long 

 Strand. Head measures 1,4X0,6 nini, the abdominal part 2 mm, 

 the neck 2 X 0,8 mm. The smaller of the two worms which seems 

 sexually immature has a much smaller abdominal part. Anterior 

 sucker obliquely perforated, behind it the opening of the uterus 

 which runs back into the abdomen. Thin grey cords seen there 

 represent the ovary. Eggs yellow, brown, reniform 0,026 X 0,005 mm. 



Taschenbeeg adds, pharynx oval, intestine present. The two 

 individuals of one cyst grow together into a roundish structure 

 with two heads. Length 6 mm X 4,5 mm. 



Many others have described this worm. Wagener mentioning 

 3 types and Ariola separating 3 species which he assigns to 2 new 

 genera Didymocystis and Didymostoma as follows: ^ 



Didymocystis rcniformis (Wagener's second form). 



Animals in each cyst similar to one another. The two regions 

 of body sharply demarcated, posterior sac like, anterior filiform 

 3—4 mm long and enlarged anteriorly. Mouth small, terminal with 

 double muscular pharynx but no sucker, short Oesophagus and two 



