STUDIES OX THE ECTOPARASITIC TREMATODES OF JAPAX. 19X 



42 on the right and only 23 on the left side; breadth 0.075-0.227 mm. 

 Habitat — Gill of Stromateus argenteus (Jap. Mana-gatsuwo). 

 Lecalitij — Mitsugahama. 

 Date— August 1889. 



5. Microcotyle truncata, n. sp. 

 ■(PL II, figs. 1 & 2 ; PI. Ill, fig. 6 ; PI. V, fig. 7.) 

 Body about 3.3 mm. long, slender, pointed anteriorly, and ending 

 posteriorly with a truncate, triangular caudal disc. Common genital 

 opening on the same level with the point of bifurcation of the alimentary 

 canal; genital atrium armed with twenty rods about 0.13 mm. in length,'^ 

 arranged in a circle which is incomplete on the dorsal side. The 

 S-shaped ovary is situated in the front half of the body, the hinder 

 end lying at the middle of the whole length of the body. Its anterior 

 third is large, but its posterior two-thirds are slender, and it pre- 

 sents a slight enlargement at the posterior end which is in close 

 contact with the foremost testes. The single, median, dorsal vaginal 

 opening is situated a little more anteriorly than midway between the 

 common genital opening and the front end of the ovary. Vaginal 

 canal goblet-shaped, the mouth of the goblet corresponding to the ex- 

 ternal vaginal opening, and the bottom communicating with the paired, 

 yolk-ducts. These, proceeding backwards, unite with each other at 

 about the level of the front end of the ootyp, and open into the 

 oviduct midway between the origin of the oviduct and the beginning 

 of the ootyp. Tlie genito-intestinal canal opens into the oviduct just 

 opposite the yolk-duct. The vitellaria of the two sides are quite dis- 

 tinct both in front and behind, reaching in the former region up 

 to the very point of bifurcation of the alimentary canal. Here also the 



1). The apparent difference of length iu fig. 2, PI. II, is, as stated in the anatomical 

 part, probably due to the fact that the ventral ones are looked at not quite perpendicularly to 

 their long axes. 



