262 



BULLETIN OF THE BUREAU OF FISHERIES. 



of identifying the principal periods, however, is necessary, if we are to follow the course 

 of development and the changes which attend the molt. Fortunately two guideposts 

 are always present at either end of the series, the lock spine (fig. 12 L) and a distal 

 spur or tubercle on the lower side of the propodus near its tip (Sp.) For convenience 

 of description we assume, then, that the first period lies proximal to the spur, and that 

 the "lock" spine is the primary member of a hypothetical fifth period. Between these 

 boundaries lie three, four, or exceptionally five, periods, of which the fourth is rarely 

 perfect. This leaves three or at most four periods (numbered in all the figures i-iv) 

 for special consideration. 



Counting the tip of the claw as a primary spine (though it really is not, since it 

 develops as a seta), we should have from five to seven periods between it and the lock 



J*«rioAJI. 



Fig. II. — Diagram to show tlie serial arrangement of the spines in the toothed forceps of the lobster in periods of 8, and 

 the development of these spines by interpolation from the first to the fourth stages. Arabic ntimerals indicate orders 

 of teeth (here reading from left to right). 



spine. Proximal to the lock spine, the Unear series is completed by from three to five 

 primary teeth, with small secondary spines among them, which Uke similar spines else- 

 where are a fluctuating quantity. Consequently in the propodus there are from 8 to 

 12 primary spines which represent periods, of which never more than 3 or 4 are com- 

 plete, or in eights. (Compare fig. 29.) 



In order to set these relations in clearer light as well as to illustrate individual 

 variation I append a table of formulae for the teeth in the large segment of the toothed 

 claw of 10 lobsters taken at random (table 6), and of the teeth before and after the 

 molt in the claw of an adolescent (no. 11 a, 116, stages Vii and viii) and an adult animal 

 (no. 12a and 126). 



