IKiLOTIiriUA. 27 



to tlu- nei-liU.iiriiii: jwd,and it seems capable of great expansion and 

 powerful eonlrartion. 



Tin- respiratory apparatus is farther displayed by two large tubular 

 trunks, extending nearly six inches from a common tube connected with 

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

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

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

 municates likewise to all the common tubes. 



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

 very ituliMinet flaccid portions are represented in some treatises, or 

 nit her simple notices of tin- animal. 



Thus the respiratory apparatus obviously constitutes a great portion 

 of the internal contents of the body, 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 an i main 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 Goad by, the 

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

 Plate VL 



In the living object, however, while the vital functions are ad van - 

 chui. this organization is more amply developed, being distended farther, 

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

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

 respiratory tree protruded from the wound. It now resembled a great 

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

 junction and communication being quite perceptible through the diapha- 

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



turgid, sometimes becoming a little flaccid. \> iy portion endowed 

 with vitality, as demonstrated by their enrvature, especially at the ex- 

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



rt Knox, lie immediately pronounced the protrusion part of the 

 respiratory organs. The rupture being an inch abme the terminal >ri 



