110.~——~Dr. F. Miller on the Metamorphoses of the Prawns. 
the frontal margin even in the oldest Nauplius. They appear at 
first as delicate, nearly globular, limpid vesicles (fig. 30), but 
subsequently as minute, firmer, and more opake mammiform 
appendages to the anterior margin of the ocular peduncles 
during the whole period of larval life (fig. 8 0). 
The new segments, on which the thoracic and abdominal feet are 
afterwards developed, form at first an unjointed, soft, short zone, 
which, however, soon becomes elongated. Before this zone at- 
tains the length of the section of the body lying behind it, a 
division into eleven segments may be detected, although at first 
this is not very distinct. At first these segments are of nearly 
equal length, or the anterior ones may even be longer and more 
distinctly separated ; but towards the end of this period the five 
posterior ones form about one-third of the entire length of the 
body, whilst the six anterior scarcely constitute one-ninth of it, 
the remainder of the length being half before and half behind 
these new segments*. The five posterior new segments (abdo- 
minal segments) acquire a short spine at the hinder margin in 
the middle of the back, and the last of them also one on each 
side. Of internal parts, only the intestine is at first clearly 
distinguishable in these new segments; the ganglionic chain 
is afterwards developed, and it is only towards the end of this 
period that the muscles become separated into sharply defined 
bundles. 
The new appendages sprout from the ventral surface of the 
corresponding segments at first in the form of simple lobes, 
which, however, soon show a longer external and shorter internal 
branch. At first, and indeed when the separation of new seg- 
ments just begins to be perceptible, the third pair of footjaws 
and the lateral lamine of the caudal fan are produced; at a 
much later period the five pairs of thoracic feet make their ap- 
pearance at once. Before the conclusion of this period, the 
branches of the footjaws acquire fully developed sete, but still 
remain unjointed ; the thoracic feet continue rudimentary and 
destitute of sete. The lateral caudal lamin which are attached 
directly (without a joint) to the basal joint, acquire a few short 
* Whether the first of these eleven rings is already present (as I believe 
to be the case) at the commencement of this period—in other words, 
whether all the eleven, or only ten, segments are really to be indicated as 
new—I must leave undetermined. In the latter case, we should have,— 
in the first period (Nauplius) five original segments (antenne, mandibles, 
tail) and the formation of five new ones (for the maxille and footjaws) ; ~ 
in the second period (Zoéa) the formation of 2 5 new segments, of which 
some (thoracic segments) acquire rudimentary feet in this period, and the 
others (abdominal segments) only in the third period (Myszs-form). This 
simple relation, however, so far from applying generally, would not even 
suit all the species of the genus Peneus. 
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