98 BULLETIN OF THE BUREAU OF FISHERIES. 
a dead sponge-bearing crab being surrounded and devoured by a multitude of young 
crabs about the size of the fingernail and the assumption that these young had just 
hatched from her sponge and then turned about and were devouring her. From the 
description, given in the following paragraph, of the young immediately after hatching, 
it will be seen that it would be impossible for them to devour a hard-shelled adult 
crab, even though observation were lacking to disprove the notion. 
The young of the blue crab, after hatching, pass through two stages before assuming 
the true crab shape.?_ In the first stage a young crab is known as a zoéa. The zoéa is 
virtually microscopic in size, measuring about 1/25 of an inch in length. From Plate 
LI, figure 21, it will be seen that in this stage the crab is much unlike the adult form. 
The body is somewhat cylindrical in shape, the eyes large and conspicuous, the spines 
at the sides short; there is a long curved spine on the back; the claws are lacking; and 
the abdomen is long and round, ending in a sort of forked tail. The zoéa has a long, 
sharp beak, two pairs of antennz, and four pairs of leglike appendages. The true legs 
have not yet appeared. The zoéa swims backward by very rapidly jerking the abdo- 
men up against the lower side of the body. The crab in this stage is free-swimming 
and does not crawl over the bottom, as it does in the later stages. The zoéa increases in 
size only when it molts. At the present time, however, it is not known how many 
moltings occur before the second stage is reached.? At each molting the new form 
resembles a little more closely the next stage. 
The crab in the second stage is known as a megalops (PI. LI, fig. 23). It is 
still very small, being less than 1/25 of an inch in width. The megalops more nearly 
resembles the adult, having a rather flattened body and an abdomen shorter and wider 
than that of the zoéa. ‘The eyes, however, are as yet more prominent than in the adult, 
and the two posterior legs are not flat, but rounded, and each is provided with a sharp 
point. The abdomen is not curled against the under side of the body, as is the case in 
the adult. The megalops swims freely and, also, may walk on the bottom. It is as yet 
unknown how many times the megalops molts before taking on the true crab shape. 
Smith and Hyman (op. cit.) found that, in the case of the rock, the green, and the 
fiddler crabs, there is only one megalops stage, the first megalops molting directly into 
the first crab stage. It is quite probable that this is true also of the blue crab. 
Whether or not this is the case, there does come a molting at which the megalops 
suddenly assumes a shape very similar to that of the adult, except that the width of the 
body is not much greater than the length, and the eyes are borne on larger and thicker 
stalks. This creature may be called the first crab. The crab, as well as the preceding 
forms, increases in size only at the time of molting. Up to the present time no one 
has observed a crab as it passes through all the different molts involved in its life history. 
Certain stages, however, of the lives of several different crabs have been observed, so 
that a fairly accurate estimate can be made of the number of moltings which occur and 
the time required for the crab to reach the adult stage. 
a The description of the first two stages of the young crab is abridged from the Handbook of Invertebrate Zoology, W. K. 
Brooks, published by S. E. Cassino, Boston, 1882. 
> Paulmier, op. cit., p. 135, estimates the number of moltings to be probably six, but gives no data upon which to support 
his claim. 
Smith, S.,in The Invertebrate Fauna of Vineyard Sound, U. S. Fish Commissioners’ Report, 1873, found that there are four 
zoéal stages in the green crab of the Atlantic coast. 
Hyman, O. W., in a yet unpublished paper found that the fiddler crab passes through five zoéal stages. 
