Lepeophtheirus dissimulatus — Lewis 
239 
TABLE 6 
Mean Length of Attachment Filament 
CHALIMUS 
COPEPODITE 
1 
2 
3 
4 
5 
6 
Measurement (in mm) 
0.136 
0.111 
0.146 
0.156 
0.155 
0.163 
0.213 
Number of specimens 
1 
6 
30 
13 
60 
7 
2 
distally than proximally; the lateral margins are 
flatly convex, the distal surface almost flat and 
bearing three simple although well-developed 
spines. The innermost of the three terminal 
spines is longest, the outermost shortest. 
The make-up of the fourth thoracic leg of 
the sixth chalimus is similar to that of the adult 
(Fig. 20#) although the armature is more sim- 
ple. The segments of the adult, particularly the 
distal three, are more elongate; the terminal 
spines on each segment have at least one den- 
ticulated or frilled margin and are encircled by 
a frilled process at their base. 
Caudal Rami 
The caudal rami are first present in the co- 
pepodite stage (Fig. 12 a). These structures, in 
the copepodite, are slightly more than one-half 
of the greatest length of the combined genital 
segment and abdomen and their greatest width 
is approximately equal to the length. Both of 
the lateral and the distal margins are irregular. 
Two short, plumose setae are present on the 
proximal one-half of the outer lateral surface 
and two long, plumose setae arise from the distal 
surface. 
The caudal rami of the first chalimus (Fig. 
12b) arise from the posterior ventral surface of 
the genital-abdominal segment. The greatest 
length of the rami is approximately two-thirds 
of the width; the lateral and distal margins are 
continuous. Six plumose setae are present on 
the rami, two on the distal lateral surface, three 
on the distal surface, and one on the inner distal 
corner. 
The caudal rami of the remaining chalimus 
stages and the adult (Fig. 12c-/) are similar 
in shape and make-up to the rami of the first 
chalimus. Minor differences such as the setula- 
tion of the inner margin in the second chalimus 
(Fig. 12c) and succeeding stages and a varia- 
tion in the length of the setae are the only sig- 
nificant changes that occur after the first chal- 
imus. 
REMARKS ON BEHAVIOR OF DEVELOPMENTAL 
STAGES AND THEIR RELATION TO HOST 
Both of the planktonic first and second nau- 
pliar stages exhibit a strongly positive photo- 
tropism in the laboratory. Movement in both of 
these stages is sporadic and jerky, the three pairs 
of appendages present on each of these stages 
moving in unison in a series of strokes and then 
remaining motionless for a short period of 
time. The animal thus makes a short but swift 
movement and then rests, sinking gradually. 
Whether it is the response to light or a more 
intrinsic factor that controls the amount of time 
spent in swimming and in resting was not de- 
termined. The function of the balancers present 
on the posterior end of the nauplii has been 
suggested to be the balancing of the nauplius 
when it is at rest (Wilson, 1905:538). Since 
these structures were not seen to move to any 
extent in L. dissimulatus, their function cannot 
be definitely ascertained although their structure 
and position do suggest that they play a role in 
the positioning of the nauplius during both 
movement and rest. 
As the age of the second nauplius increases, 
the positive reaction to light decreases, a condi- 
tion that extends into the planktonic phase of 
the copepodite. A light placed on one side of a 
finger bowl caused some copepodites to swim 
towards that side. The tendency, however, was 
not as great as in the naupliar stages and ap- 
peared to diminish as the age of the copepodites 
increased. The movement of the copepodite was 
quite rapid although jerky and irregular; the 
periods of time spent in swimming were longer, 
and the time spent in resting shorter than in 
either of the two naupliar stages. During the 
resting phase the copepodite appeared to sink 
