408 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
with the caudal part, bring pressure to bear on the anterior end of the shell and 
on other parts. Rupture was never observed to take place elsewhere than at the 
anterior end. When the shell has ruptured, with the leverage afforded on all sides, 
the larva is half out in a second or two; then with a single effort the shell is slipped 
off from the ends of the appendages and the nauplius swims freely about. 
The nauplius in this stage (tig. 10) measures 0.213”*“ in length. Of the three 
pairs of swimming appendages the two posterior are biramous, the rami of the third 
being very short. The first appendage bears 6 spines; the second, 5 and 6 on the 
anterior and posterior rami, respectively, besides the rudiment of the “masticatory 
blade” ( rnasc . 1)1.) on the protopodite; the third bears 2 on the anterior ramus, 3 on 
the posterior, and 2 or 3 short spines on the protopodite and posterior ramus. The 
spines are straight and without branches that could be seen with the power used. 
In addition to the other parts referred to in the description of the egg-nauplius, 
the alimentary canal (al. can.) can here be traced for the greater part of its course. 
Alongside of it are seen two stout muscles (ms. th. ab.) attached anteriorly and 
dorsally to the carapace in the region of the third appendage; posteriorly they seem 
to be inserted on the ventral side of the thoraco-abdominal part, and I assume them 
to be the means of the antero- ventral flexures of that section of the body observed 
in the act of hatching, and when the nauplius is kept from swimming by light 
pressure on the, cover-glass. The parts indicated by x are perhaps muscles to the 
mouth region, but they were not so clear that muscular structure was evident. The 
position of the long frontal horns (fr. A.) bent posteriorly subparallel to the sides of 
the body is characteristic of this stage of the nauplius. 
To obtain nauplii for study or preservation, ripe-looking barnacles may be 
selected and teased as described above. It was found better, however, to keep one 
or two dishes of water, each containing thirty or forty barnacles; the water need be 
changed only every two or three days. The nauplii aggregate at the surface and 
toward the brightest light, and can be obtained at almost any time, but, as the first 
molt occurs very soon, they are almost all in the second stage. De Filippi states 
that the nauplii of D. darwinii remain near the ovisacs for a long time, undergoing 
further development there (’01, p. 75, and ’61 a, p. 203). The first nauplii of D. mulleri 
often at least, probably as a rule, leave the branchial chamber early, undergoing the 
first molt outside. Washing out the gill chamber of the crab has never yielded 
more than a very few nauplii; when they pass from the capitulum of the parent they 
must be carried at once out of the crab’s gill chamber. 
The length of time between the hatching and the first molt was not definitely 
determined, but it was evidently very short — probably usually within an hour. In 
one case, when a barnacle was teased on a slide and nauplii in the act of hatching 
were found in the drop on the slide and others already free, two or three vigorous 
larvae of the first stage (fig. 10) were transferred to a watch glass of water. Fifteen 
minutes later a nauplius was observed to have the frontal horns projecting forward, 
to have the appendages placed parallel to the axis of the body, and to be evidently 
longer than when first observed. The appendages were pressed more and more 
closely against the sides, and slight twitching motions of the body and appendages — 
apparently shrugging first one shoulder, then the other — were accompanied by a 
gradual lengthening of the body to 0.387"’"', by which time it could be seen that the 
