File:Image from page 123 of "Introduction to zoology; a guide to the study of animals, for the use of secondary schools;" (1900) (14804841493).jpg

Identifier: introductiontozo00dave Title: Introduction to zoology; a guide to the study of animals, for the use of secondary schools; Year: 1900 (1900s) Authors: Davenport, Charles Benedict, 1866-1944 Davenport, Gertrude Anna Crotty, 1866- Subjects: Zoology Publisher: New York, Macmillan company London, Macmillian and co., ltd. Contributing Library: MBLWHOI Library Digitizing Sponsor: MBLWHOI Library

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Text Appearing Before Image: of the oesophagus, stomach,and intestine as well, since these organs are formed by aninfolding of the skin. By means of the return of the bloodto the limbs and rapid absorption of water, the body of thelobster soon swells to a size far beyond that of the old shell.There remains in the stomach, after moulting, a calcareousnodule which has long been known by the name of crabs-eyes. These crabs-eyes were formerly much sought 104 ZOOLOGY after and prized on account of their supposed medicinalqualities. The function of these gastroliths or craVs-eyes was for a long time rather obscure. It is nowbelieved that during the time of absorption of lime fromthe shell, previous to moulting, the blood becomes stronglyimpregnated with lime. If all the lime that must be re-moved were to remain in the blood, it would probably befatal to the animal; hence it is taken up by secreting cellslocated in the wall of the stomach, and there deposited.After the old skin is cast, the gastrolith is soon absorbed,

Text Appearing After Image: FIG. 90. —Palasmonetes vulyaris, a common shrimp. Nat. sizo. Photo.by W. H. C. P. probably to aid in strengthening the new shell. Bits ofwater-worn shells, entire gastropod shells, parts of lobstercoverings, spines of sea-urchins, etc., have been found inthe stomachs of lobsters and crayfish, which likewise wouldprobably have been dissolved and used in hardening theshell. Shrimps and prawnsl belong to a thin-skinned, long-tailedfamily of Crustacea.2 They are extremely common in bays 1 These are common names of small Crustacea applied chiefly to thedecapod family Carididse,* although also applied to certain Schizopods.The term shrimp is applied to the smaller species, and prawns to thelarger. 2 Fig. 90. * (capis, a small marine crustacean. THE CRAYFISH AND ITS ALLIES 105 along our coast, and even penetrate into rivers. Two rivershrimps l are found in the United States east of the Missis-sippi River. These Crustacea are able to maintain theirenormous numbers only by virtue of their gr

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