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PACIFIC SCIENCE, VoL XVII, April 1963 
mens, 0.14 mm average for 30 adult specimens). 
The general shape, however, is the same. 
The frontal organ in the adult (Fig. 13^) is 
greatly reduced, being visible only as a small 
opaque area on the median longitudinal axis of 
the body just posterior to the groove dividing 
the frontal region from the cephalothorax. The 
attachment filament is completely absent, the 
only indication of its previous presence being 
the circular scar mentioned with reference to 
unattached specimens of the sixth chalimus. 
Antennule 
Throughout development, from the nauplius 
to the adult, the antennule is two-segmented. 
The changes that occur in this appendage are 
changes in the general shape and relative size 
of the segments in addition to changes in the 
armature. 
The antennule of the first nauplius (Fig. \Aa) 
is uniramous and is attached to the anterior 
ventral lateral surface of the body. The lateral 
Fig. 13. Frontal region of developmental stages of L. dissimulatus. Ventral view of anterior surface: a, 
Copepodite; b, first chalimus; c, second chalimus; d, third chalimus; e, fourth chalimus; f, fifth chalimus; g, sixth 
chalimus; h, adult. A-l, Antennule; A-2, base of second antenna; FO, frontal organ; FP, frontal plate; R, 
Rostrum. 
