Entozoa of Hn'tish Marine Fishes. 79 



and has a diainetor ol" ll-'^.'? nun. Botli arc circular in 

 outline with circular apertures. 



Tlic alimentary system is well developed. Tlic mouth 

 opens into a long pre-pharynx (about '.'J mm. lonj^ in an 

 average specimen), which is followed by a pharynx of large 

 size {')i\ x-l(5 mm.) ; the oesophagus is very short and the 

 diverticula into whii'h it divides arc of great width and 

 extend to the end of the body. 



The excri.tm'y vesicle is a simple sac of no great extent, in 

 the posterior end of the i)o(ly and opens by a terminal pore. 



The testes are median, one behind the other, in the pos- 

 terior third of the body. They are globular or ovoid in 

 shape and of considerable size (25 mm. diameter). The 

 edge of the posterior testis is at a distance of about "0 mm. 

 from the end of the body. The o\ary lies directly in 

 front of the tistes and is much smaller than tliem. The 

 reccptaculum seminis is an elongated vesicle lying between 

 the ovary and the anterior testis. The vitelline glands are 

 extensive and well-defined ; situated laterally from the level 

 of the ventral sucker to the posterior extremity of the body. 

 They consist of numerous, compact, irregular follicles. 



The ova are few in number (about .')()) and are confined to 

 the space bounded by the ovary, the ventral sucker, and the 

 two intestinal diverticula. Light yellow in colour, ovoid 

 in shape, they measure 'OoU-'UGH mm. in length and 

 •033--U10 mm. in breadth. 



The genital a|)erture is in front of the ventral sucker, but 

 to the left of the middle line; it is within the intestinal 

 fork. The sphincter muscle surrounding it is sometimes 

 very prominent. 



The penis-sac (PI. I. fig. 4) is of large size and divi !cd 

 into two portions ])y a constriction. The anterior part is 

 the penis-sac proper, containing the retracted jicuis and the 

 prostate, neither of which is very large. This part is 

 regularly ovoid and lies in front of aud dorsal to the ventral 

 sucker. Joined to this by a luirrow neck is a large sac con- 

 taining a long rather narrow vesicula scminalis. This sac is 

 capable of considerable extension and contraction, and' iu 

 the latter state the vesicula scminalis becomes bent up, as is 

 shown in the figure. There is a short non-prostatic ()art of 

 the ductus ejaculatorius issuing from the anterior end of the 

 seminal vesicle. 



Linton describes a form from Gadiia callanus, which lie 

 identities as Distomum rachion, Cobbold, or a species very 

 near it. His description is short, but the measurements lie 

 notes for the various organs show a remarkable a;rreemcnt 



