338 BULLETIN OF THE BUREAU OF FISHERIES. 



Slighter structural changes which appear upon closer examination of the second 

 larva are as follows: The rostrum is broader and its margins are serrated; the sides of the 

 carapace completely cover the giUs and separators ; the sixth pair of abdominal append- 

 ages, the uropods of the tail fan, can be seen through the transparent cuticle as rudiments 

 at the base of the telson ; the stalk of the antermule is divided into three segments as in 

 the adult, and its inner secondary flagellum, which is present in the first larva as a minute 

 bud on the lower side of the primary flagellum, is much larger and shows traces of seg- 

 mentation, while the stouter primary branch bears on its iimer margin numerous clusters 

 of sensory hairs. The long terminal spine of the outer flagellum has disappeared; the 

 second antenna shows a reduction in its exopodite, the outer leaf-like scale with fringe 

 of plumose hairs, which progresses with the following molts, and an extension of its 

 segmented whip or endopodite; the chelae or double claws borne on the first three pairs 

 of walking legs are more perfect, and those of the first pair, which are destined to become 

 the big claws of the adult, are perceptibly larger but otherwise similar. Both of the 

 "great claws" gradually develop into the primitive toothed type, reached in the fourth 

 stage, with teeth arranged in periods of eight; the primary and secondary spines only 

 are present in the second larva. (See ch. vii.) Average length of second larva, Woods 

 Hole, Mass., 9.3 millimeters; extremes, 8.3 to 10.2 millimeters (47 measurements); stage 

 period, 2 to 5 days; Wickford, R. I. (Hadley), average length, 9.6 millimeters; average 

 duration of stage period, 3 days; extremes, 2 to 7 days. 



THE THIRD LARVAL STAGE. 

 [Fig. 42.] 



Molting for the second time after hatching, the larva enters upon its third free 

 swimming stage, in which the exopodites of the six pairs of thoracic legs (segments ix- 

 xiv) are still functional. In habits, in color, and in general appearance the first three 

 stages in the pelagic life of the lobster show no striking differences. The third larval 

 stage, however, is readily distinguished from the second by the larger size of the animal, 

 the presence of the completed tail fan, and the less rudimentary condition of the swim- 

 merets upon the second to the fifth abdominal somites. The telson is reduced, though 

 relatively much longer than the uropods; its terminal border is still incurved as in the 

 first larva, but its lateral spines are longer. The inner whip in both antermse is rela- 

 tively larger and distinctly segmented, that of the second pair being considerably larger 

 than the scale. 



The " big" claws, though somewhat larger, still conform to the same type. They pre- 

 sent a series of uniformly spaced spines, corresponding to the largest teeth of the lock- 

 forceps or toothed claw of the adult, with rudimentary intermediate spines of the sec- 

 ond order, or, if the latter are not present, the ducts of tegumental glands only, which 

 mark their future position, may appear on the surface of the shell. 



Like the earlier larvse, they swim with head pointed downward, and with incurvated 

 tail when rising, falling, or moving either forward or backward in the water, and 

 they dart rapidly backward by sudden flexions of the tail. Yet Hadley observes that 



