THE AMERICAN LOBSTER. 
199 
The sex can not he determined by the abdominal appendages alone until after the tenth 
molt. In two lobsters, 35 and 36.3 mm. long respectively (Nos. x, xi, table 39), which 
bad probably molted twelve times, we have no difficulty in deciding from the structure 
of the abdominal appendages (represented by figs. 86, 87) that the first is a female, 
the last a male. 
The gradual growth of the appendages of the first abdominal somite is illustrated 
in table 39. In a lobster 2 inches long (51.8 mm.) these have a length of about an 
eighth of an inch (or 3 mm.). 
Table 39 . — Progressive stages in the development of the appendages of the first abdominal somite. 
No. 
Number in tables. 
No. of 
molt. 
Length 
of lob- 
ster. 
Length of 
first ab- 
dominal 
appendage. 
Sex. 
Remarks. 
mm. 
mm. 
I 
(36, table 34) 
5 
14 
•0. 11 
2 
* II 
(36, table 34) 
6 
16 
.27 
2 
III 
6 
16.3 
2 . 10 
1 
V' 
(34 table 34) 
7 
18 
2 
2 
IV 
8 
19.3 
.27 
Male 
See fig. 90, plate 32. 
VI 
(37, table 34) 
8 
19. 75 
. 2 
Female . 
See fig. 80, plate 32. 
VII 
(3, table 34) 
8 
21.2 
.25 
Female . 
See figs. 85 and 89, plate 32. 
VIII 
(38, table 34) 
10 
26.6 
3 1.5 
2 
Appendage not segmented. 
IX 
(34, table 34) 
10 
29. 50 
3 2 
2 
Appendage consists of two minute joints. 
X 
(17, table 33) 
3 12 
35 
2 
Female . 
See fig. 86, plate 32. 
XI 
(18, table 331 
3 12 
36. 3 
2. 30 
Male 
See fig. 87, plate 32. 
XI I 
(1 table 32) 
40.3 
2. 60 
XIII 
(19, table 33) 
51.8 
3.04 
Female . 
See fig. 88, plate 32. 
1 Tubercle. 2 Bud. 3 Not accurately determined. 
Second , third, fourth, and fifth pleopods. — The condition of these appendages in the 
second, third, and fourth larval stages is illustrated by figs. 93, 94 and 97, plate 33. Each 
appendage consists in the second larva of a stalk with the blade-like endopodite and 
exopodite. Rudimentary fringing setae are developed after the third molt, but the 
appendage is but little longer and otherwise unchanged. In the fourth larva (fig. 97) 
the natatory appendages come immediately into use. The long fringing setae grow 
out and the limb itself is almost double its former size. 
The telson and “ tail f an f — The flat telson of the older embryos is deeply cleft 
into two lobes (fig. 72), which bear on their free terminal edges short interlocking 
setae. The bifurcate condition of the embryonic telson, which recalls very forcibly that 
of a protozoea and is jirobably the remnant of a former larval condition, is retained up 
to the time of hatching and is lost only with the molt preceding the first larval stage. 
After the first molt the telson appears as a broad, triangular plate (plate 19, and 
plate 34, fig. 103) joined immovably to the abdomen and admirably adapted for 
swimming. By the aid of this paddle the animal darts rapidly backward with every 
flexion of the abdomen. The dorsal surface of the plate is convex, and its posterior 
margin is incurved and armed with spines and stout plumose setre, as shown in the 
drawing. 
The sixth pair of abdominal appendages, which, as already mentioned, are clearly 
outlined beneath the cuticle of the second larva (fig. 102,, become broad lamellar pad- 
dles in the third stage (fig. 104), and in the fourth larva nearly equal the telson in length 
(fig. 105). The outer lamella is jointed at its posterior end and bears on its upper 
surface, near the line of the articulation, a short median tooth, as in the adult state. 
After the fourth molt the caudal-fan is very similar to that of the adult. The telson is 
