Trematode from Protopterus. 87 



latter does not interfere at all with the natural contour of the 

 body externally, but its aperture is very easily seen, and it is 

 not difficult under a dissecting-microscope to insert a tine 

 needle into it and to see that it passes forward without 

 resistance into the sac. This large opening appears to be 

 the aperture of the excretory apparatus, the terminal portion 

 of which is probably represented by the sac. 



Internal Anatomy. 



Alimentary Canal. — The oral sucker leads into a very 

 short prepharynx, surrounded by a cluster of "salivary" 

 glands. This is immediately followed by the almost spherical 

 muscular pharynx, 0T8 mm. in length, and this again by a 

 quite short oesophagus, dividing at once into two widely 

 divergent intestinal CEeca. The latter are unbranched, and 

 extend nearly as far as the posterior end of the body and 

 considerably beyond the yolk-glands, maintaining about the 

 same width throughout. 



Genital Organs. — As already observed, the genital pore is 

 situated very far towards the left side of the body, and at 

 some distance in front of the ventral sucker. It leads into a 

 small common " atrium," at the base of which, side by side, 

 are the openings of the cirrus-sac and vagina. The cirrus- 

 sac is large and muscular, the muscles being arranged 

 longitudinally. It takes a dorsal direction at first from its 

 opening, then curves ventrally and over to the left side, 

 ending behind or slightly to the left of the posterior edge of 

 the ventral sucker. It contains a long eversible penis, which 

 is apparently unarmed. The distal portion of the cirrus-sac 

 is lined with large, conspicuous, and deeply staining " pro- 

 static " cells, which extend back to the level of the ventral 

 sucker. The inner end contains a voluminous vesicula 

 seminalis, divided by a constriction into a larger proximal 

 and a smaller distal portion. The latter has a well-developed 

 coat of circular muscle-bands. Immediately in front of it 

 there is a small oval " pars prostatica/' 



The two testes are unequal in size and asymmetrical in 

 position. Both are elongate and sausage-shaped, with entire 

 margins, but the right testis is almost twice as long as the 

 left, the measurements being about 0'85 mm. and 0*5 mm. 

 respectively. The anterior end of the right testis is in close 

 contact with the ovary, and it extends backwards nearly as 

 far as the posterior limit of the vitelline glands on that side. 

 The left testis is situated somewhat further forward, beginning 



