200 BULLETIN OF THE 
The abdomen is relatively no larger than in adult specimens, and is bent 
underneath against the sternum. The telson consists of a single piece, with a 
faint indication of the median suture of the adult. After the next moult the 
diagonal sutures appear (Fig. 8) and the telson assumes the polymeric charac- 
ter of the adult.* The posterior border of the telson is fringed with long and 
delicate ۰ 
The first pair of antennæ (Figs. 3, 6 b) have an enormously developed basal 
(auditory) segment (Fig. 3 a), followed by a three-jointed peduncle bearing two 
flagella (0, c), of which the outer (c) is the longer. 
The second pair of antenns are very long (longer than in the adult), com- 
posed of about thirty-four segments. 
The oral appendages have almost exactly the structure of the corresponding 
appendages of the adult, which are represented on Plate III. Figs. 13-18, 
The mandibular palpus has attained its perfect, tri-articulate structure, and is 
as large in relation to the size of the body of the mandible as it is in the full- 
grown specimens, This is remarkable when one considers its rudimentary 
form in the last zoéa-stage (Plate II. Fig. 8 a). 
The chelipeds are longer than in the adult (Fig. 11). One (commonly the 
right) is larger than its fellow. Like the four following pairs of thoracic legs, 
they are beset with sete on either border. 
The ambulatory pairs are also longer than in the adult, The dactylus 
(Fig. 4) is armed with hooks like those in the full-grown specimens (Fig. 19), 
but it is much more slender. 
The posterior thoracic legs are rudimentary and terminated with a didactyle 
claw (Fig. 5), as perfectly formed as in the adult. 
The second, third, fourth, and fifth abdominal segments bear peculiar two- 
branched appendages (Fig. 10), furnished with long, feather-like sete. The 
large number of individuals which I examined (which it is fair to presume 
included both sexes) showed no difference in the number and shape of the 
appendages of the abdomen. In the adult these appendages take on a very 
different form in both sexes. In the female they become one-branched, slender 
organs (Fig, 20), and the pair belonging to the second segment disappears.F In 
the male only one pair persists (on the second segment, Fig. 21) ; here the 
second branch exists as a rudiment (a). The series of changes through which 
the abdominal appendages of the young are converted into the adult form 1 
as unhappily unable to follow. In specimens from South Carolina, 6 mm. 
across the carapace, the external sexual characters are already acquired. 
My specimens underwent but little change, before I left Newport in Septem- 
* Milne Edwards thought that the sutures in the telson of Porcellana showed that 
it was formed by a consolidation of the seventh abdominal segment with a pair of 
appendages belonging to the same segment (Histoire Naturelle des Crustacés, I. 
p. 249. 1837) It is plain from the development that this theory of the structure 
of the telson is false. 
+ In the adult females of many species of Porcellana tho first, second, and third 
abdominal segments are destitute of appendages. 
