Mesostephanus appendiculatus — Martin 
with bristles. Tubular glands are plentiful lat- 
erally and sparse dorsoventrally in the anterior 
half of the body. Ten to 12 glands have their 
cell bodies near the oral sucker and have ducts 
opening near the mouth. Measurements based 
on 20 stained and mounted specimens are: body 
length 0. 18-258, av. 0.192; maximum body 
width 0.078-.115, av. 0.094; oral sucker length 
0.031-045, av. 0.038; oral sucker width 0.025- 
.037, av. 0.03; ventral sucker midventral, ru- 
dimentary, 0.009-012, av. 0.01 in diameter; 
lengths of prepharynx and esophagus approxi- 
mate that of pharynx; pharynx oval to spherical, 
0.006-012, av. 0.011 long and 0.012-.016, av. 
0.013 wide; intestinal caeca sinuous, termi- 
nating near excretory bladder; genital primord- 
ium median, immediately anterior to excretory 
bladder, 0.006-.022, av. 0.019 long and 0.019- 
.025, av. 0.021 wide; excretory bladder small, 
transversely elongate, with exit duct entering 
tail, dividing into two ducts which pass around 
the "Island of Cort” and rejoin, extending to 
the furcal region to divide into two ducts, each 
of which opens to the outside at the tip of a 
furca. Four collecting ducts empty into the blad- 
der, two laterally and two medial to the lateral 
ducts on the anterior wall of the bladder. The 
two medial ducts pass around the genital pri- 
mordium to unite and proceed as a single duct 
to a point near the bifurcation of the gut where 
it joins the lateral ducts which have proceeded 
anteriorly from the bladder. As the lateral ducts 
bend medially, each gives off a duct whose prox- 
imal portion contains a tuft of cilia. The latter 
duct extends posteriorly to about mid-body level 
where it divides into anterior and posterior 
branches each of which collects from three 
groups of three flame cells each. Three of the 
flame cells emptying into the posterior branch 
are located in the tail. The excretory formula is 
2 [(3 + 3 + 3) + (3 + 3+ (3)] = 36. Short, 
moniliform concretions occur in the main col- 
lecting tubes. The tail is set in a dorsal socket 
near the posterior end of the body. The tail 
surface bears bristles and minute spines. The 
tail stem length is 0.3 58-407, av. 0.376, and 
maximum width near the junction with furcae 
0.0 14-022, av. 0.021. The furcae are 0.18-.2, 
av. 0.19 long and 0.019-022, av. 0.021 in maxi- 
mum width near the junction with the tail 
279 
stem. Each furca bears a dorsoventral fin over 
the distal four-fifths of its length. 
METACERCARIA: Fundulus parvipinnis parvi- 
pinnis and Gillichthys mirabilis were exposed 
to cercariae which rapidly penetrated the skel- 
etal muscles and encysted. Penetration of large 
numbers of cercariae killed the fish. Death of 
the second intermediate host due to the pene- 
tration of large numbers of cercariae has been 
noted by Vernberg (1952) for a related par- 
asite. Metacercariae approximately 3 weeks old 
were dissected from the fish and were fed, along 
with some muscle tissue, to hatchery-raised 
chicks. 
ADULT ( Fig. 1 ) : Adult Mesostephanus ap- 
pendiculatus were obtained from the small in- 
testines of hatchery-raised chicks fed fish mus- 
cle and metacercariae. The chicks were exam- 
ined 9 days after the experimental feeding. The 
following description and measurements are 
based on nine specimens. Body surface covered 
with scale-like spines arranged quincuncially. 
Body length 0.547-763, av. 0.68; body width 
0.346-518, av. 0.41; oral sucker length 0.04- 
.059, av. 0.049; oral sucker width 0.047-.078, 
av. 0.055; acetabulum 0.04-.068, av. 0.06 in 
diameter; tribocytic organ well developed, open- 
ing usually slitlike; prepharynx very short; 
pharynx 0.037-.058, av. 0.05 long and 0.031- 
.044, av. 0.037 wide; esophagus approximately 
one-half pharyngeal length, with transverse mus- 
cle fibers; intestinal caeca sinuous, with occa- 
sional short diverticula, reaching to near pos- 
terior end of body; testes oblique, in posterior 
half of body, 0.109-124, av. 0.116 long and 
0.072-.087, av. 0.079 wide; cirrus sac and cirrus 
well developed; male genital opening communi- 
cates with common genital exit at posterior end 
of body; ovary intertesticular, 0.05-.08, av. 0.065 
long and 0. 04-065, av. 0.05 wide; metraterm 
elongate, muscular, with sphincter at distal end 
where it empties into common genital exit; eggs 
yellow, operculate, 0.084-.137, av. 0.108 long 
and 0.058-.081, av. 0.07 wide; vitellaria com- 
posed of discrete follicles arranged in a circle 
in posterior half of body but not entering pos- 
terior conical body extension; excretory system 
more complex than in cercaria, anastomosing 
branches arise from main collecting ducts, some 
branches end blindly near body surface. 
