THE AMERICAN LOBSTER. 



199 



The sex can not be determined by the abdominal appendages alone until after the tenth 

 nolt. In two lobsters, 35 and 36.3 mm. long respectively (Nos. x, xi, table 39), which 

 Lad probably molted twelve times, we have no difficulty in deciding from the structure 

 of the abdominal appendages (represented by figs. 80, 87) that the first is a female, 

 the last a male. 



The gradual growth of the appendages of the first abdominal somite is illustrated 

 in table 39. In a lobster 2 inches long (51.8 mm.) these have a length of about an 

 eighth of an inch (or 3 mm.). 



TABLE 39. — ■ Progressive stages in the development of the appendages of the first abdominal somite. 



No. 



Number in tables. 



No. of 

 molt. 



Length 

 of lob- 

 ster. 



Length of 

 first ab- 

 dominal 



appendage. 



Sex. 



Remarks. 



I 



11 



III 



(36, table 34) 



(36, table 34) 



13.1 mlilo 34l 



5 

 6 

 6 



7 

 8 

 8 

 8 

 10 

 10 

 3 12 

 3 12 



mm. 

 14 

 16 



16.3 

 18 



19.3 

 19.75 

 21.2 

 26.6 

 29.50 

 35 

 36.3 

 • 40.3 

 51.8 



mm. 

 •0.11 

 .27 

 2 .10 

 .2 

 .27 

 .2 

 .25 

 3 1.5 

 3 2 

 2 



2.30 

 2.60 

 3.04 



i 



See fig. 78, plate 32. 



See fig. 84, plate 32. 



See fig. 82, plate 32. 



See fig. 83, plate 32 (bud without joints) . 



See fig. 90, plate 32. 



See fig. 80, plate 32. 



See figs. 85 and 89, plate 32. 



Appendage not segmented. 



Appendage consists of two minute joints. 



See fig. 86; plate 32. 



See fig. 87, plate 32. 



See fig. 91, plate 32. 



See fig. 88, plate 32. 



t 



j 



V (34 fabln 341 



t 



IV 





Male.... 

 Female . 

 Female . 

 i 



VI 

 VII 



VIII 



IX 



X 



XI 



XII 



XIII 



(37, table 34) 



(3, table 34) 



(38, table 34) 



(34, table 34) 



(17, table 33) 



(18, table 33) 



(1 table 32) 



i 



Female . 



Male 



...do .... 



Female . 



(19 table 33) 









1 Tubercle. 



2 Bud. 



' Not accurately determined. 



Second, third, fourth, and fifth pleopods. — The condition of these appendages in the 

 second, third, and fourth larval stages is illustrated by figs. 93, 94 and 97, plate 33. Each 

 appendage consists iu the second larva of a stalk with the blade-like endopodite and 

 exopodite. Eudimentary fringing setae are developed after the third molt, but the 

 appendage is but little longer and otherwise unchanged. In the fourth larva (fig. 97) 

 the natatory appendages come immediately into use. The long fringing setae grow 

 out and the limb itself is almost double its former size. 



The telson and " tail-fanP — The flat telson of the older embryos is deeply cleft 

 into two lobes (fig. 72), which bear on their free terminal edges short interlocking 

 setae. The bifurcate condition of the embryonic telson, which recalls very forcibly that 

 of a protozoea and is probably the remnant of a former larval condition, is retained up 

 to the time of hatching and is lost only with the molt preceding the first larval stage. 



After the first molt the telson appears as a broad, triangular plate (plate 19, and 

 plate 34, fig. 103) joined immovably to the abdomen and admirably adapted for 

 swimming. By the aid of this paddle the animal darts rapidly backward with every 

 flexion of the abdomen. The dorsal surface of the plate is convex, and its posterior 

 margin is incurved and armed with spines and stout plumose setae, as shown in the 

 drawing. 



The sixth pair of abdominal appendages, which, as already mentioned, are clearly 

 outlined beneath the cuticle of the second larva (fig. 102,, become broad lamellar pad- 

 dles in the third stage (fig. 104), and in the fourth larva nearly equal the telson in length 

 (fig. 105). The outer lamella is jointed at its posterior end and bears on its upper 

 surface, near the line of the articulation, a short median tooth, as in the adult state. 

 After the fourth molt the caudal-fan is very similar to that of the adult. The telson is 



