198 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
fifth stage they are represented by small rounded tubercles (fig. 78, plate 32). At this 
time there are no external characters by which the sex of the individual can be deter- 
mined with certainty. 
In the sixth stage (fig. 95, plate 33; lobster No. in, table 39) this appendage 
consisted of a small bud (0.1 mm. long); after the seventh molt (larva 18 mm. long) 
its length was doubled (tig. S3). 
In lobster No. Vi (table 39) this appendage in tbe eighth stage (larva 19.75 mm. 
long) was a simple bud of about the same dimensions (fig. 80). 
In another young lobster, probably a male in the eighth stage (length, 19.3 mm., 
fig. 901, the appendages of the first abdominal somite are similar to those of the seventh 
and eighth stages just referred to. 
In another case, that of a lobster in sixth stage (No. ii, table 39, fig. 84, plate 32, 
length of lobster 10 nun.), this appendage was about equal in size to those just 
described. In still another lobster (No. vi, table 39), which was followed from the 
fourth stage onward through four molts, this appendage is a little larger and is 
partially segmented (fig. 85, plate 32) in the eighth stage. The under surface of the 
thorax of this lobster is shown in fig. 89, plate 32, where the openings of the oviducts 
are clearly seen, thus determining the sex. 
In a young female 35 mm. long (No. x, table 39) this appendage measures 2 mm. 
and is composed of two joints (with possibly a small coxal segment) of about equal 
length (fig. 86). The distal joint is constricted into a number of smaller segments and 
bears a few very minute setae. When the female is 2 inches long the first pair of 
abdominal limbs have attained the length of only 3 mm. (fig. 88, plate 32). The 
appendage is exceedingly slender and, as in earlier stages, is devoid of pigment. The 
peripheral segment is multiarticulate and is fringed with fine, short hairs. 
In a male 36.3 mm. long (No. xi, table 39) the appendage, though very minute 
(2.3 mm. in length), has the same shape as in the adult. It consists of a two-jointed 
protopodite, a minute coxa and long basis, and a grooved distal segment (fig. S7). In 
a lobster but little larger (No. xn, table 39), length 40.3 mm., the appendages of the 
first abdominal somite are similar, blit a trifle longer. As shown in the drawing of 
the under side of the thorax of this lobster (fig. 91, plate 32), they nearly meet on the 
middle line. 
We see that the appendage of the first abdominal ring may assert itself either in 
the sixth, seventh, or eighth stages. The buds are developed on the posterior margin 
of the sternum of the first abdominal somite, and in the early period of their growth lie 
facing each other, transverse to the long axis of the animal (fig. 95, plate 33). These 
minute delicate appendages do not at first show any trace of pigment. After seg- 
menting into two joints the appendage becomes elevated from the surface of the somite 
into a nearly vertical position. 
The sex can be determined as early as the eighth stage, but not, as Professor Ryder 
supposed, by the appearance of the appendages of the first abdominal ring. At this 
stage these vary from 0.20 to 0.27 mm. in length, and may or may not be segmented into 
two joints (figs. 80, 85, 90). It is only by the openings of the sexual ducts that the sex can 
be distinguished at the eighth stage. The under surface of a female in the eighth stage 
(21.2 mm. long, No. vn, table 39) is shown in fig. 89, plate 32. The openings of the 
oviducts were discernible, and the development of the sterna of the last and penulti- 
mate thoracic segments which enter into the formation of the seminal receptacle is 
slightly different from the conditions seen in the male. 
