344 
BULLETIN OP THE BUREAU OF FISHERIES. 
meet. The microscopical rudiments of the swimming exopodites have been further 
reduced but do not, as a rule, wholly disappear until the sixth stage. Average length 
at fifth stage, Woods Hole, Mass., 14.2 mm.; extremes, 13. 4-15 mm. (15 measurements); 
stage period, n-18 days; Wickford, R. I. (Hadley for 1904), average length, 15.5; 
stage period, 9.5 days. 
THE SIXTH STAGE. 
[PI. XXXII. ] 
The sixth-stage lobster resembles the preceding stage in all essential respects both 
in structure and behavior, barring the fact that apparently all or nearly all animals 
in this period are bottom inhabitants. In color the two stages are nearly identical 
and subject to a similar range of variation. The tendon marks, and the cream-colored 
or dull-white spots on the tips of some of the appendages, which begin to show as early 
as the fourth stage, are even more pronounced than before. There is a prominent 
light spot at the distal extremity of the fourth podomere of the great chelipeds, as 
already mentioned for the fifth stage. 
The modified abdominal appendages of the first abdominal somite commonly 
appear in the fifth or sixth stages as minute tubercles or buds, which at first lie upon 
the sternal surface across the long axis of the body, thus facing each other or pointing 
toward the middle line. After segmenting into two divisions, which in some cases 
does not happen until the eighth stage, this appendage becomes bent downward until 
it stands at nearly right angles with the underside of the tail. I was not able to deter- 
mine the sex by the abdominal appendages alone until the tenth stage, but Hadley 
(124) maintains that this distinction can be made in the eighth or ninth stages, or even 
as early as the sixth or seventh stages, by means of the position of the openings of the 
sexual ducts. My material did not enable me to fix the sex by means of these ducts 
earlier than the eighth stage, but this was not extensive, and it can not be doubted 
but that in all such matters considerable individual variation exists. 
The development of the crusher type of claw or the transition from the symmetrical 
to the asymmetrical condition of the great chelipeds begins in the sixth or seventh 
stage, and is marked by a blunting to be later followed by a fusion of the teeth to form 
crushing tubercles, but the change proceeds very slowly and is not conspicuous for 
some time. The future crusher gains at first in girth or breadth rather than in length 
(see ch. vii, p. 271). Average length at sixth stage, Woods Hole, Mass., 16. 1 mm.; 
extremes, 16-17 mm. (12 measurements); stage periods, 14 days. Wickford, R. I., 
average length, 18.6 mm. (12 measurements); stage period, 12.7 days. 
THE SEVENTH STAGE. 
The seventh stage is sometimes distinguished from the sixth period, as already 
remarked by the first noticeable differentiation of the crushing and toothed claws, but 
aside from this there are no characteristics in size, form, or function by which this and 
subsequent stages can be distinguished with certainty unless one has watched and 
recorded every molt. 
