174 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



Another larva (11 mm. long) has colors similar to the first just described: Large 

 chelae 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 iu an important 

 degree bj^ the greater or less time which has elapsed since the last molt — that is, by the 

 greater or less proximity to the ecdysis 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 the 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, " 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 61 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 chelae 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 chela?. 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 be 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. 



