692 Variations in a Copepod Crustacean, (September, 
bead, forming a tier (originally several connate segments), and 
another larger, semi-segmented joint with a terminal, inner, bent- 
backward hook, and finally two smaller terminal joints. The di- 
lated joints as well as some of the narrower preceding joints, are 
armed with powerful spines, and others 
with bristles. If this swollen right an- 
tenna be separated from a live male, it 
will twist around with snake-like mo- 
I / 
/ 
i 
WHY tions for several minutes. 
| | ( As the external structures, with the 
\\ exception of the fifth thoracic seg- 
. : ment, the anterior antenne, the fifth 
\ \\ 4 pair of legs and the abdomen, are 
\\ alike in both sexes, we may proceed 
; N \\ to the posterior or second pair of an- 
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\ \ 
tennze (see Fig. 3). 
The posterior antenne originate 
from the second pair of larval legs and 
have like those two branches. They 
are destined for locomotion, and 
also for respiration. The main branch 
is slightly shorter than the secondary branch. ; 
Having once with certainty recognized the mandible (Fig. 4), 
then, after applying higher powers (about 500 X), we are enabled 
to see the following characters: 
The tip of the first (outer) tooth 
is bent and has a very minute 
excavation. There are eight 
mandibular teeth. The second 
tooth is larger than any of the 
remaining six of the series, 1ts 
suddenly contracted tip some- 
what bent like the first tooth; 
it is separated from the third by 
an interval equal to the width 
1G. 4.—Mandible and mandibulary of the tooth. A. short stiff 
palpus. Enlarged about 300 x. bristle appears at the lower end 
of the row of teeth. The secondary appendage of the mandibu- 
lar palpus is four-jointed and bears six delicate bristles at its tip 
and inner margin. The larger, bent-upward bristle near the inner 
\ 
Fic. 3.—Posterior or second 
antenna. Main branch shorter. 
