262 
bulletin oe 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 
Sta^ A. 
J*eriodJ. I^eriodJI. 
Fig. II. — Diagram to show the 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 numerals indicate orders 
of teeth (here reading from left to right). 
spine. Proximal to the lock spine, the linear series is completed by from three to five 
primary teeth, with small secondary spines among them, which like 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 formulse 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. iia, iifo, stages vii and viii) and an adult animal 
(no. 12a and 126). 
