Natural history of the American lobster

9781231054024: Natural history of the American lobster
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 Excerpt: ...vii, p. 259), and if any further evidence were needed to show that the breaking joint, which is functional up to the fourth stage, corresponds to the articulation of the second and third segments, it would seem to be furnished by Emmel's discovery of a missing flexor muscle at this point. While autotomy does not normally occur before the fourth stage, the limbs are often snapped off at the joint destined to become the breaking plane. Lobsterlings occasionally cast a claw at the articulation between the second and third segments which 'has the appearance of a free joint; fusion is not completed until the fifth stage, from which time onward autotomy in its typical form becomes a common occurrence. An interesting adjustment to prevent excessive loss of blood in the stump of the reflexly amputated limb has been described by Emmel (97). We have seen, in referring to his account in another place (ch. vi, p 245), that as the venous sinus crosses the breaking plane it is divided into two channels by a septum in which are lodged the two arteries and two nerves of the limb; on the proximal side of the joint the septum gives off two folds, which are swung out by blood pressure after the break occurs and acting as valves to the small openings exposed, check the bleeding at once. It would appear from Emmel's work that the severed arteries must immediately contract so that their blood is discharged proximally to the folds or valves which he describes. Whether a similar adjustment to prevent excessive loss of blood is found in the other appendages, so far as I am aware, has not been determined. To continue this account further, when a claw is shot, a short jet of blood is thrown from the stump, but the bleeding soon ceases, followed by a slight swelling of the tissues ove...

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