18 THE HANCOCK PACIFIC EXPEDITIONS VOL.2 



icr to midbody. Seminal vesicle elongated sac-like from acetabulum 

 to near ovary; pars prostatica about as long as vesicle, straight; 

 ductus hermaphroditicus a simple muscular tube as long as pars 

 prostatica. Ovary globular; Mehlis' gland posterior to ovary; semi- 

 nal receptacle anterior to ovary; uterus between testes and acetab- 

 ulum; eggs 88 to 102 by 48 to SO/x; vitellaria from ovary to pos- 

 terior end, confluent behind testes. Excretory vesicle extending to 

 testes; 2 pairs of anterior and 1 pair posterior collecting tubules. 

 Lymph vessels well developed, much branched, apparently funda- 

 mentally 2 pairs of longitudinal stems forking to form 4 pairs along 

 much of body length. Type host: Cheilichthys annulatus. Other host: 

 Spheroides angusticeps, a related fish. Type locality: Galapagos 

 Islands. 



The name longisinosum refers to the long genital sinus. 



Comparisons. A. longisinosu77i is more than twice larger than J. 

 mexicanum and the body is relatively wider. The aperture of the 

 acetabulum is longitudinal rather than transverse. The vitellaria do 

 not nearly reach the acetabulum as they do in J. mexicanum, a dif- 

 ference correlated with the larger uterus in A. longisinosum. In A. 

 longisinosum the genital sinus is much longer; the eggs much larger 

 (maximum length 102 ^i compared with 67 p.) ; the lymph vessels 

 more branched anteriorly. In spite of these differences the species 

 are very similar and clearly congeneric. 



There are genera of the Allocreadiidae with the cirrus sac weak- 

 ly developed or lacking, for example the Anallocreadiinae and 

 Opecoeliinae, but Apocreadium diff'ers from most in its tubular geni- 

 tal sinus and from all in its lymphatic system. It is probably signifi- 

 cant that the Anallocreadiinae which lack a cirrus sac also possess 

 a tubular genital sinus described as "a common tube" in the form 

 of an "unspecialized cloacal invagination" by Simer (1929, p. 564) 

 for Anallocreadium armatum; as a "long genital sinus" by Manter 

 (1926, p. 87) for Homalometron pallidum; as "an invaginated clo- 

 aca" by Hunter & Bangham (1932, p. 138) for Anallocreadium pear- 

 sei; but as a "genital atrium" by Manter (1936, p. 34) for Crassi- 

 cutis cichlasomae. In this latter case however, the "atrium" may be 

 tubular in form. 



The genus Apocreadium then shows evidence of relationship to 

 the Anallocreadiinae. On the other hand, however, its lymphatic 

 vessels, the structure of the pharynx and the excretory system sug- 



