NATURAL history OF AMERICAN LOBSTER. 
269 
successful would increase the serial number to 16. A few cases are noted of the intro- 
duction of a tooth of the sixth series (table 6, no. 8, 116). The process of interpolation 
is illustrated in the diagram (fig. ii) up to the usual 8-period stage, which is commonly 
attained at the fourth or fifth molt. 
Fig. 19 —Outline of corresponding part of great claw shown in figures 17 and 18, but at third larval stage, showing 
spines of the second order, sometimes preceded by ducts of glands (d 2a, and d 2b), interpolated between those of the 
first, also spur (sp) and tip of claw (< s). both of which arise like the setae, and like the teeth are provided with 
glands, the ducts (d t g) of which open at their summits. Compare figure ii. 
The first teeth to appear apparently occupy the same plane, but at the seventh 
stage, or even before this, the alignment is similar to that of the adult claw, and the 
future “lock spine” or tooth (L in all the figures) is readily distinguished by its form and 
position. 
It is interesting to notice that in all the early larval stages and up to at least the 
fifth or sixth molt, each serial tooth is regularly pierced by the canal of a single tegu- 
Fig. 20.— Outline of corresponding part of big claw represented in figures 17 to 19, but at fourth stage, showing spines of the 
third and fourth orders, and the establishment of a single period of 8, though the identity of the periods in this case 
can not be exactly defined. luvaginated claw tip still bears duct of gland (d t g), and the spur UP) is still invaginated 
like a hair. 
mental gland (fig. 17-20), which opens on its proximal side and just below the summit. 
In some cases the opening of the duct precedes the spine and marks its future position 
exactly (fig. 19 b). While the serial spines are always developed as outgrowths of 
the skin, the tips of the claw (fig. 17-20, t. s.) and peculiar tubercle or spur {sp. in all 
figures) originate like ordinary hairs, and like them are always invaginated previous to 
