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PACIFIC SCIENCE, Vol. XX, July 1966 
a part of the osmoregulatory system, but con- 
nections between them and the excretory canals 
were not clearly distinguished. 
Fig. 3. Posterior end of a female worm, showing 
the posterior vestigial ovary. 
Fig. 4. A, Ova from an anterior ovary; B, ova 
from a posterior ovary. Immature ova in an anterior 
ovary appear similar to those in B. 
One of the important diagnostic characteris- 
tics of the family Camallanidae, as listed in the 
literature, has been a blind posterior branch of 
the uterus. The posterior ovary in Spirocamal- 
lanus istiblenni (Fig. 3) is normally much 
shorter than the anterior ovary, and it contains 
cells that appear similar to the immature ova in 
the first portion of the anterior ovary (Fig. 4). 
The posterior ovary is probably vestigial, and 
thus appears to represent a last stage in the 
evolutionary progression toward the elimination 
of one ovary. The large, coiled, anterior ovary, 
plus the oviduct, reaches a maximum length of 
about 10 mm, or half of the total body length. 
The oviduct narrows before it enters the ex- 
panded seminal receptacle (Fig. 5), which it- 
self narrows before entering the large, thin- 
walled uterus. At this latter junction the walls 
contain glandular cells. In one of the nine fe- 
male worms the long, functioning ovary is not 
anterior in position, but is posterior, and the 
seminal receptacle expands to form the posterior 
horn of the uterus. 
The male caudal papillae are grouped as 
shown in Figure 6, and the alae curve anteriorly 
to meet ventrally. The two spicules bear a length 
ratio of 3:2 (Figs. 6, 7). In both male and 
female worms the lower part of the intestine 
and the rectal gland are supported by conspicu- 
ous muscle fibers (Figs. 6, 8). In the male the 
anus is surrounded by four small papilla 2 
(adanal), a condition not uncommon in this 
genus. The posterior finger-like tip of the body 
has from zero to three minute projections. 
Two excretory canals run the entire length 
of the worm, and join at about the level of the 
glandular esophagus to form an excretory sinus 
