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. 83). 



In lobster No. VI (table 39) this appendage in the 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. 90), the appendages of the first abdomiDal 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. n, table 39, fig. 84, plate 32, 

 length of lobster 16 mm.), 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 seta?. 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. 87). In 

 a lobster but little larger (No. xn, table 39), length 40.3 mm., the appendages of the 

 first abdominal somite are similar, bat 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. SO, 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. 



