File:Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct - for the use of schools and colleges (1870) (14780417514).jpg

Identifier: outlinesofcompar00agas (find matches)
Title: Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges
Year: 1870 (1870s)
Authors: Agassiz, Louis, 1807-1873 Gould, Augustus A. (Augustus Addison), 1805-1866 Wright, Thomas, 1809-1884
Subjects: Physiology, Comparative Zoology
Publisher: London : Bell & Daldy
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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mbraneis incessantly renewed, and respiration thereby maintained. (In the Echinidce (fig. 174), the space comprised betweenthe viscera and the test is filled with water, which is drawninto and rejected from the body by five pairs of mem-branous respiratory tubes, collected into ten tuft-like organs,situated around the circumference of the oral aperture, andopening internally by two perforated pits, as in Asterias.The water thus introduced into the interior of the testHows along the membrane, covering its surface, and overthe peritoneal layer, investing the digestive organs andtubular feet and ovaria by the action of cilia, so that the in-terior of thetest of theEchinus is in-cessantly tra-versed by re-spiratory cur-rents, whilstthe blood,circulatingthrough the coriaceous in-tegument, isin like man-ner aerated bycurrents flow-ing over itssurface by thevibrations ofcilia. In the Ho-lothuria (fig.232), the re-spiratoryfunction islimited to apair of or-gans formedafter a typewhich attains
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Fig. 232.—The anatomy of the Holothuria tnbuio a. 218 OF RESPIRATION. its full development, among the air-breathing vertebrata, in-stead of entering the general visceral cavity by tubes, andflowing over the surface of the peritoneum by the motionsof cilia, as in the Asteriadae and Echinidce; the water isinspired through a single chamber, called the cloaca (g, fig.232) ; and by the contraction of its muscular walls flowsinto two tubular branched organs (i, k\ attached by a process ofthe peritoneum to the walls of the body ; upon the membra-nous lining of these organs, which divide and subdivide, likea tree, into branches, terminating in tuft-like cells (in) ; theblood-vessels ramify like the pulmonary vessels on the bron-chial tubes in the air-breathing vertebrata, which they furtherresemble in the rythmic movements of dilatation and contrac-tion, which take place three times in a minute in the Holo-thuria tubulosa (fig. 232), the water, after each inspiration, re-maining about twent

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