Lepeophtheirus dissimulatus^-LEWlS 
209 
both the fifth chalimus and the adult but which 
was present on all of the female sixth chalimus 
specimens examined. 
The genital segment of the male sixth chali- 
mus (Fig. 12^) is longer than that of the fe- 
male; the greatest width is approximately three- 
fourths the greatest length. The lateral margins 
are flatly convex, angled slightly from a swelling 
on the anterior lateral corner, comparable to the 
nodelike formation on the female, to the widest 
point in the region of the fifth legs. The poste- 
rior region of the segment curves medially from 
the region of the fifth legs to the abdomen. Both 
the fifth and sixth legs are lobate, the fifth ap- 
proximately one-half the length of the sixth. 
The fifth legs project from the ventral lateral 
surface of the posterior one-half of the segment 
and possess a single plumose seta on the ante- 
rior end of the outer margin and three plumose 
setae on the distal surface, an increase of one seta 
from the fifth chalimus. The sixth legs project 
from the ventral surface just inside and poste- 
rior to the fifth legs and extend posteriorly to 
the posterior end of the segment. A single plu- 
mose seta, absent in the preceding chalimus, is 
present on the distal one-half of the outer mar- 
gin of the sixth legs and two plumose setae are 
present on the distal surface. 
The one-segmented abdomen of both sexes 
(Fig. 12^?, i) is short, approximately one-third 
the length of the male genital segment; the 
length is exceeded somewhat by the width. The 
anterior end is slightly narrower than the pos- 
terior, the outer margin angled slightly from 
the anterior end to the middle of the segment. 
The posterior surface tapers from the middle of 
the segment to the bilobed anal region at the 
posterior extremity. 
The frontal organ (Fig. 13g) appears to have 
degenerated from the previous stage and now 
consists of two oval bodies contiguous on the 
median longitudinal axis of the body just pos- 
terior to the division between the frontal region 
and the cephalothorax. These two bodies are 
connected to the frontal filament in attached 
forms or to the circular depression in unattached 
forms by a slender, rod-shaped structure. The 
digestive tract is the same as that of the pre- 
ceding stage. 
Only one specimen survived from the moult 
into the sixth chalimus to the moult into the 
adult. The time spent by this single specimen 
in the sixth chalimus was somewhere between 
24 and 30 hr at a temperature of approximately 
23 C. 
After moulting from the sixth chalimus to 
the adult, the last moult in the life history, all 
of the appendages and processes remain un- 
changed. As seen in Figures 2-7, pertaining to 
the growth of L. dissimulatus, the maximum 
size of the male is almost completely attained 
by the sixth chalimus stage while that of the 
female not until the animal is well into the 
adult stage. Inasmuch as copulation takes place 
shortly after the terminal moult, the male would 
be more likely to be near its maximum size in 
the last larval stage. During the reproductive 
portion of the females life, eggs are stored in 
the genital segment before they are extruded, 
causing this segment to swell considerably. As 
the female does not start to ovulate until some 
time after fertilization, the significant increase 
in size after the sixth chalimus is due, to a con- 
siderable extent, to the enlarged genital segment 
as is indicated in Figures 6 and 7. The presence 
of eggs in the genital segment also pushes the 
fifth legs laterally and, in some instances, ob- 
scures them in a dorsal view of the animal. 
The cephalothorax of the adult female and 
male (Fig. 11a, b) is ovoid; the frontal region is 
distinct, separated from the cephalothorax by a 
trilobed groove. The lateral margins of the ceph- 
alothorax are convex and possess a distinct mem- 
branous flange. The posterior sinuses are distinct 
and of a shallow V-shape. The median thoracic 
region extends posteriorly slightly past the pos- 
terior extension of the lateral regions, forming 
the junction of the cephalothorax and the fourth 
pedigerous segment. The major cephalothoracic 
grooves are similar to those of the sixth chali- 
mus; two minor grooves also extend posteriorly, 
for a short distance, from the junctions of the 
lateral and median lobes of the trilobed groove 
separating the frontal region from the cephalo- 
thorax. The rodlike strengthening regions are 
more heavily sclerotized than those of the sixth 
chalimus but are similar in shape and are in the 
same position. 
The fourth pedigerous segment of the fe- 
male and male is short; the lateral regions are 
drawn out at the fourth leg as in the preceding 
stage. The terminal portions of the lateral ex- 
