NATURAL HISTORY OF AMERICAN I.OBSTER. 



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, 11&). The process of interpolation 

 is illustrated in the diagram (fig. 11) up to the usual 8-period stage, which is commonly 

 attained at the fourth or fifth molt. 



FlG- 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 (rf za, and d zV), interpolated between those of the 

 first, also spur UP) and tip of claw (i s), both of which arise like the seta;, and like the teeth are provided with 

 glands, the ducts (rf ( g) of which open at their summits. Compare figure ir. 



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. Invaginated claw tip still bears duct of gland (rf / p), 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. 1 9 cP V). WhUe 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 



