174 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Another larva (11 mm. long) has colors similar to the hrst just described: Large 
ch else reddish-brown; lower half of the abdomen, caudal fan, and sixth abdominal seg- 
ment of same color; carapace yellowish -green, rather less transparent than in earlier 
stages; bright peacock-green with yellowish tinge on the terga of the fourth and fifth 
abdominal segments; considerable blue at the joints of the appendages (probably 
because the cuticle is here thinner) and in different parts of the body. It must be 
remembered that the transparency of the larva is now determined in an important 
degree by the greater or less time which has elapsed since the last molt — that is, by the 
greater or less proximity to the eedysis which is to follow. The old cuticle becomes 
partially opaque as soon as any lime is deposited in it, which happens at about this 
period. 
The third larval stage lasts from two to eight days. 
THE FOURTH STAGE. 
The young larva 1 emerges from its fourth molt into a form which bears such a 
striking resemblance to the adult lobster that an intervening stage between this and 
the preceding was supposed to exist; but such is not tbe case. A dorsal view, colored 
to life, of one of these larvae is represented by plate 23. The swimming branches of 
its thoracic legs have been abruptly shed, or rather have been reduced to functionless 
stumps (plate 31, figs. 74, 75). It still swims at the surface, with greater agility and 
speed than at any former stage, and is still virtually a larva, although it has the adult 
locomotor organs. 
It swims rapidly forward by means of the swimmerets, and darts backward 
with quick jerks of the abdomen, “ frequently jumping out of the water in this way,” 
as Professor Smith says, u like shrimp, which their movements in the water much 
resemble” (182). As they move forward they hold the large chela: extended straight 
in front of the head; when disturbed they raise the chelae to defend themselves like 
an adult lobster. 
It has the larval rostrum and the large antennal scale or exopodite, and the 
first abdominal somite is without trace of appendages. 
The average length of 64 larvae was 12.6 mm., or about half an inch, the extremes 
being 11 and 14 mm. 
COLOR. 
The range of variation in color is now very great. A typical color pattern is rep- 
resented in plate 23. Occasionally, even at this period, a larva is very light-colored 
and its transparency is nearly equal to that of the third larva. 
The cast of color maybe (1) yellow and red; (2) red; (3) green; (4) green and 
reddish-brown. In the first case the carapace is light yellow, translucent, and sprinkled 
with red chromatophores. The abdomen and large chela: are reddish-brown, and there 
is a quadrilateral yellowish-green area on the terga of the fourth and fifth abdominal 
segments. In the red individuals the animal is bright red, especially on the abdomen 
and large chelie. The carapace is yellowish, spotted with red, and the abdomen is 
marked in the way just described. In the green variation, the whole animal is bright 
1 The use of the word “larva” for the fourth and fifth stages is not without objection, hut it is 
perhaps better than the phrase “ adult-like form.” It is very probable, as I have shown, that the 
young lobster may remain at the surface of the ocean, even after the sixth molt. It will he most 
convenient, however, to define the larval period of the animal by the duration of its pelagic life, 
which is practically at a close by the end of the fifth stage. 
