HOLOTHURIA. 27 



to the neighbouring parictes, and it seems capable of great expansion and 

 powerful couti-action. 



The respiratory apparatus is farther displayed by two large tubular 

 trunks, extendhig nearly six inches from a common tube comaected with 

 the cloaca, and diverging upwards into irmumerable lesser channels, with 

 obtuse extremities ; the whole also secured by tendons to the neighbour- 

 ing parietes. An intestinal organ, here divided and turned back, com- 

 municates likewise to aU the common tubes. 



AU these parts constitute what is called the respiratory tree, whereof 

 very indistinct flaccid portions are represented m some treatises, or 

 rather simple notices of the animal. 



Thus the respiratory apparatus obviously constitutes a great portion 

 of the internal contents of the bod}', where it is distended by water, 

 whence the oxygen may be disengaged. 



The exact powers by which both the physical and mechanical func- 

 tions are effected in such animals merit the profound attention of the 

 skilful physiologist. 



The beautiful structure of the respiratory tree is favourably repre- 

 sented here, from an excellent preparation by Mr Henry Goadby, the 

 same accomphshed naturalist to whom I am indebted for the others. 

 Plate VI. 



In the Uving object, however, while the vital functions are advan- 

 cing, this organization is more amply developed, being distended farther, 

 and exhibiting considerable action. The side of a specimen of the Holo- 

 thuria, somewhat exceeding medium size, having ruptured, part of the 

 respii'atory tree protruded from the wound. It now resembled a great 

 assemblage of ccBca, if I may so speak, all anastomosing, the reciprocal 

 junction and conmunication being quite perceptible through the diapha- 

 nous membrane, and the transparence of its contents. The whole was 

 very turgid, sometimes becoming a little flaccid, every portion endowed 

 with vitahty, as demonstrated by their curvature, especially at the ex- 

 tremities. On shewing this subject to a distinguished anatomist, Dr 

 Robert Knox, he immediately pronounced the protrusion part of the 

 respiratory organs. The rupture being an inch above the terminal ori- 



