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. Natural history of the American lobster... Decapoda (Crustacea); Lobster fisheries. 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 pr

. Natural history of the American lobster... Decapoda (Crustacea); Lobster fisheries. 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 pr Stock Photo
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Central Historic Books / Alamy Stock Photo

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PG1TDY

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7.1 MB (210.8 KB Compressed download)

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2210 x 1130 px | 37.4 x 19.1 cm | 14.7 x 7.5 inches | 150dpi

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. Natural history of the American lobster... Decapoda (Crustacea); Lobster fisheries. 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 adoles

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