a 
% i FISH ENTOZOA FROM YELLOWSTONE PARK. a00 
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sthe anterior end and a little more rapidly toward the posterior end. 
The body is marked by five longitudinal striz and a broad longitudinal 
stripe on each side; there are a few transverse wrinkles for a distance 
of about 0.3 mm. from the anterior end. The mouth appears to be 
simple and there is no w@sophagus. Another is a fragment, the pos- 
terior end of a female, length 11 mm., breadth 0.5 mm. This fragment 
is cylindrical; posterior end rather blunt. In optical section the body 
appears to be crenulated, owing to the deep transverse striw. 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, slightly-curved point, behind the 
anal aperture (Fig. 49). Head small, truncate, mouth apparently 
trilobed. Body marked by regular transverse striw, making serrate 
margins in optical sections near anterior end, the serrations becoming 
crenulate posteriorly. The @sophagus 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 tobe 4mm. Spicules, 
2, diverging. Genital aperture of female about posterior third, vulva 
prominent. My specimens do not present many characteristic details 
of structure, and I am not able, without more careful examinations of 
sections, to reach a satisfactory conclusion with regard to their classi- 
fication. 
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 with polygonal nucleated 
cells about 0.02 mm.in diameter. The body tapers abruptly at the 
posterior end, but more gradually towards the anterior end. The 
mouth appears to be three-lobed and surrounded by about five minute 
papille. The chitinous cuticle is uniformly and minutely marked with 
transverse strie. 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 mm. from the posterior end. In another 
of these encapsuled nematods, which was stouter than the ones just 
described, 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- 
