344 BULLETIN OK 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- (i5 measurements) ; 

 stage period, 11-18 days; Wickford, R. I. (Hadley for 1904), average length, 15.5; 

 stage period, 9.5 days. 



THE SIXTH STAGE. 

 [PI. xxxu.] 



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 

 Ught 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 he 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 daw 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. i 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 daj's. 



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 tmless one has watched and 

 recorded every molt. 



