FISH ENTOZOA FROM YELLOWSTONE PARK. 559 



the anterior end and ;i little inor« rapidly towaid the posterior end. 

 The body is marked by five louj^itudiual striie and ii broad longitudinal 

 stripe on each side; there are a few transverse wrinWes for a distance 

 of about 0.3 mm. from the anterior end. The mouth appears to be 

 simple and there is no (esophagus. Another is a fragment, the pos- 

 terior end of a female, length IL mm., breadth 0.5 mm. This fragment 

 is cylindrical; posterior end rather blunt. In oj)tical section the body 

 aiJpears to be creuulated, owing to the deep transverse striie. The in- 

 testine is dark brown and the anal aperture nearly terminal. 



Another species, which bears some resemblance to Ascaris tenuissima 

 Zeder, was found in the trout (Figs. 47-51). These are slender, white 

 worms, tapering- gradually towards the anterior end from about the 

 posterior third; posterior end larger except at the extremity, where it 

 tapers rather abruptly to a blunt, slig'htly-curved point, behind the 

 anal aperture (Fig. 49). Head small, truncate, mouth apparently 

 trilobed. Body marked by regular transverse stri;e, making' serrate 

 margins in ojjtical sections near anterior end, the serrations becoming 

 crenulate posteriorly. The oesophagus is short, with what I take to be 

 a chitinous ring at base. The few specimens which I have found are 

 small. The following measurements were obtained from a female, 

 dimensions given in millimeters : Length, 7 ; diameter of anterior end, 

 0.03 ; post anal diameter, 0.04 ; diameter immediately in front of anal 

 aperture, 0.06; greatest diameter of body about 0.12; ova, 0.04 by 0.02 

 in diameter. The length of a male was found to be 4 mm. Spicules, 

 2, diverging. Genital aperture of female about posterior third, vulva 

 prominent. My specimens do not xn^esent many characteristic details 

 of structure, and I am hot able, without more careful examinations of 

 sections, to reach a satisfactory conclusion with regard to their classi- 

 lication. 



Some small nematods encapsuled in the muscular walls of the intes- 

 tine of the trout were found, some of which appear to be immature 

 forms of the foregoing. These worms are very small, hardly exceeding 

 3 mm. in length, and many of them not more than 2 mm. long. One of 

 them, which measured 2 mm. in length, was 0.06 mm. in diameter, and 

 for the greater part of its length was filled Avith polygonal nucleated 

 cells about 0.02 mm. in diameter. The body tapers abruptly at the 

 posterior end, but more gradually towards tlie anterior end. The 

 mouth appears to be three-lobed and surrounded bj^ about five minute 

 pai)illce. The chitinous cuticle is uuiformly and minutely marked with 

 transverse strife. This feature in optical section produces serrate 

 margins, the teeth of which are about 0.01 mm. apart. In one the anal 

 aperture was found to be 0.2 nnn. from the iwsterior end. In another 

 of these encapsuled nematods, whi(;h was stouter than the ones just 

 des('ribed, the polygonal cells were present and also minute cells about 

 0.002 mm. in diameter, which filled a large part of the body. The 

 length of this specimen was 3 mm., the diameter 0.2 mm. In this speci- 



