Lep e op hth eiruS dissimulatus — -LEWIS 
219 
end of the second segment is slightly less than 
three-fourths of the width of the proximal end; 
the distal surface is concave with its outer por- 
tion heavily sclerotized and serving as the articu- 
lation surface for the outer proximal end of the 
third segment. The third segment and terminal 
process are similar to those of the preceding 
stage although the process is slightly longer and 
the distal portion more sharply curved. The 
adult female and male appendage is visible 
within the second antenna of late sixth chalimus 
specimens. Both parts of the bifurcate terminal 
process of the adult male can be seen (Fig. 15;) 
as well as the single female terminal process 
(Fig. 15k). 
It was earlier stated that the second antennae 
can not be used to differentiate the two sexes 
in the late chalimus of L. dissimulatus. As was 
just described, the female and the male second 
antenna are similar in the sixth chalimus, the 
last larval stage. Not until the moult from the 
sixth chalimus to the adult is there any signifi- 
cant difference between the appendages of the 
two sexes in L. dissimulatus. For this reason, the 
presence or absence of the sixth legs, found only 
in the male, was used as the major differentiat- 
ing characteristic. Additionally, in the sixth chal- 
imus, the presence of internal spermatophores 
in the male was used to verify the differentiation 
of the two sexes. 
The second antenna of the adult (Fig. 15/, m) 
is attached to the ventral surface of the cephalo- 
thorax just anterior and medial to the postan- 
tennal process and posterior and lateral to the 
base of the antennule. The first segment of the 
female is short and forms a broad articulation 
surface for the second segment. The segment 
possesses a posteriorly directed, spinelike pro- 
jection from the posterior proximal surface. The 
second segment is strongly developed, its great- 
est width being equal to its greatest length. The 
third segment is slender and heavily sclerotized, 
bearing a sharply curved, spinelike terminal 
process and two naked, seta-like accessory proc- 
esses, one from the inner surface of the proxi- 
mal region and the second from the distal lateral 
surface. The division between the third seg- 
ment and terminal process is indistinct and in- 
complete. 
The first segment of the adult male second 
antenna (Fig. 15/) is longer than that of the 
female; the segment is broader proximally than 
distally and is attached to the cephalothorax 
along the entire length of the proximal surface. 
The distal end of the first segment is small and 
two-pronged, forming an articulation surface for 
the second segment. Additionally, the major 
portion of the outer lateral surface forms an 
adhesion surface of heavily sclerotized, over- 
lapping, platelike structures. The second seg- 
ment is strongly developed, its greatest width 
slightly more than one -ha If of the greatest 
length. The outer margin of the segment is 
strongly convex proximally; the inner margin 
is irregular due to the presence of two sets of 
adhesion surfaces similar to those of the first 
segment. The inner distal margin of the second 
segment also possesses a finger-like protrusion 
that appears to be segmented but presumably 
forms an adhesion surface, and the segmented 
appearance is due to the overlapping plates. The 
protrusion is, in most specimens, curved around 
the second segment and appears as a regular 
adhesion surface but it is not attached to the 
segment except at its proximal end. The third 
segment is short and bears a bifurcate terminal 
process in addition to a single, naked, seta-like 
accessory process from the inner distal end. 
Mandible 
Comparing the over-all development of the 
three naupliar appendages, it is evident that the 
mandible has the most drastic change. Almost 
all of the change occurs in the moult from the 
second nauplius to the copepodite when the 
appendage changes from a biramous appendage 
to a uniramous, four-parted, rodlike process. The 
four-parted condition could not be traced to 
either the exopodite or the endopodite of the 
naupliar appendage. All four parts appear to 
be almost completely fused; there are no muscles 
penetrating the appendage and there is no trace 
of the second ramus of the biramous naupliar 
appendage. These three conditions make the 
analysis of the derivation of the mandible of 
the copepodite of L. dissimulatus extremely dif- 
ficult, and even with the analysis made by Hee- 
gaard (1947:59, 196-202), no hypothesis can 
be offered until further work has been done. 
The mandible of the first nauplius (Fig. 1 6a) 
is biramous and attached to the ventral lateral 
surface just posterior to the second antenna. 
