230 
PACIFIC SCIENCE, Vol. XVII, April 1963 
TABLE 2 
Armature of First Thoracic Legs of Developmental Stages* 
STAGE 
MARGIN 
PROTOPODITE 
EXOPODITE 
1 2 
ENDOPODITE 
Copepodite 
outer 
Is 
3h,lHm 
inner 
IP' 
3P,1Q 
7P 
Chalimus I 
outer 
Ip 
lp,3P 
IP 
inner 
3P 
IP 
Chalimus II 
outer 
lp 
1P,3P 
IP 
inner 
4P 
IP 
Chalimus III 
outer 
lp 
lrh 
3H 
lrh? 
inner 
Ip 
3P,1P 
? 
Chalimus IV 
outer 
IP 
lrh 
3H 
lrh? 
inner 
lp 
3P,1P 
lrh? 
Chalimus V 
outer 
lp 
lrh 
3H 
lrh? 
inner 
IP 
c 
3P,1P 
lrh? 
Chalimus VI 
outer 
Ip 
lrh 
3H 
lrh? 
inner 
lp 
c 
3P,1P 
lrh? 
Adult 
outer 
IP 
lrh 
3H,1P 
? 
inner 
IP 
c 
3P 
? 
* For explanation of symbols see Fig. 1. 
gradual change of the first thoracic leg from the 
first chalimus stage to the adult. There is a 
gradual reduction in the size of the endopodite, 
with regard to the exopodite. Both the exopo- 
dite and the endopodite are of approximately 
equal size in the copepodite but even in the first 
chalimus the endopodite is distinctly smaller 
than the exopodite, a change that is carried 
through later development until in the adult the 
endopodite is a mere rudiment, vastly smaller 
than the exopodite. The second trend is the 
gradual elongation of the exopodite segment 
from the palm-shaped copepodite segment to 
the elongate second chalimus segment (Fig. 
18/?), then the division of this segment into two 
segments in the third chalimus (Fig. 18z) and 
the later elongation of each of the two seg- 
ments, especially the proximal, to the adult con- 
dition (Fig. 18 m). 
The armature of the first thoracic leg changes 
in character more than in quantity from the first 
chalimus to the adult. The second chalimus 
exopodite bears seven lightly plumose setae on 
the distal surface and one short, lightly plumose 
seta from the middle of the outer lateral surface. 
The exopodite of the third chalimus, a two- 
segmented structure, bears three spines and one 
lightly plumose seta on the distal surface and 
three lightly plumose setae on the inner lateral 
surface of the second or distalmost segment in 
addition to a single, spinelike process on the 
outer distal lateral corner of the first segment. 
The total number of processes on both of the 
segments is the same as the number on the sin- 
gle exopodite segment of the second chalimus 
although the character is quite different. The 
armature of the exopodite remains the same as 
that of the third chalimus throughout develop- 
ment except for the addition of a row of setules 
along the inner surface of the first segment. 
The two lightly plumose setules on the distal 
surface of the endopodite segment of the first 
chalimus are found through most of the devel- 
opment (see Table 2) although distinctly re- 
duced in size until in the adult they appear as 
minute, indistinct projections from the distal 
surface of the rudimentary endopodite. One 
other change occurs in the armature of the first 
thoracic leg, the addition of a small, lightly plu- 
mose setule on the proximal inner margin of 
the protopodite segment of the third chalimus. 
Some change occurs in the shape of the first 
thoracic leg segments but these are of a rather 
minor nature and are shown in Figure 18 f~m. 
Thoracic Leg II 
The armature and character of the mem- 
branes, spines, and setae comprising the arma- 
ture are given in Table 3. 
