NATURAL HISTORT OF AMERICAN LOBSTER. 
321 
When the lobster is ready to hatch, it is therefore covered from head to foot with a 
close-fitting chitinous tunic which must be shed before active life is possible. As 
explained earlier, this outer garment sticks to the egg coverings and is kicked off when 
these are cast aside. 
Before hatching and therefore before the molt which occurs at birth, the terminal 
telson is forked, and in this respect recalls the more primitive protozoea larva, which 
has been attributed to the lobster without any further warrant than this fact; the first 
larva resembles an overgrown zoea, and the fourth corresponds in some degree to the 
megalops state of the crab. 
Since the first larval stage is preceded by a true molt, failure to pass which is often 
fatal in the operations of fish hatcheries, it has seemed best to recognize this fact. The 
molts and stages will therefore be named and numbered uniformly; molt 1 introduces 
stage no. 1, and not stage 2, according to most writers on these subjects; molt no. 4 
precedes stage no. 4, and so on. 
The first larva (fig. 34 and pi. xxviii) is about one-third of an inch long, and con- 
tinues to swim near the surface for from 3 to 5 weeks, or until the fourth (pi. xxxi) or 
fifth molt, when it sinks to the bottom and passes the remainder of its life essentially 
like an adult animal. The life of such a crustacean is thus made up of a series of stage 
periods, each of which represents the time passed between successive castings of the 
shell. The first four periods during which growth is most rapid and change most pro- 
found are passed rapidly. After this point, and particularly after the sixth or seventh 
stage, except for increase in size, there is comparatively little change from molt to molt. 
During the three early stages the larvae lack the power of very precise orientation. 
They will move steadily for a time with nicely coordinated movements, when their 
equilibrium is suddenly upset and they begin to reel or turn over completely. This 
seems to be due to the fact that their statocysts, which are the most important balancing 
organs, are not well developed until the fourth stage. 
Twins and monsters are occasionally born, a fact noted by Brightwell in 1835, but 
this seldom if ever occurs under normal conditions. (See ch. viii, p. 287.) In two cases 
of twins observed by Anderton in the European species one larva was released earlier 
than the other, which continued to rotate in the egg until set free. 
The following changes in structure and instincts take place at the fourth molt 01 
beginning of the fourth stage, which marks the most surprising leap in the whole history 
of development: Loss of the primitive swimming branches of the thoracic appendages; 
the cuticle becomes shell-like, containing more lime; the pigments are denser, the colors 
brilliant, and the color pattern variable; otocysts are present and orientation is perfect; 
rotation of great forceps is complete; the animal, during at least a part of this stage, 
moves toward the light and swims steadily at the surface with great claws directed 
forward and held close together; the preying instinct is more marked; the fighting 
instinct, the instincts of fear, “feigning,” and hiding are all developed at the beginning 
or close of this stage or in the fifth, which follows, when the animal goes to the bottom 
to stay. 
48299° — Bull. 29 — 11 21 
