104 LECTURE IX. 



The oesophagus (b) divides into four canals (c), which enter the 

 base of four processes (p, p), which are continued from the centre 

 of the under part of the animal's body. These peduncles divide 

 and subdivide like the roots of a plant ; the oesophageal canals 

 follow these ramifications, and ultimately terminate in numerous pores 

 (d, d), upon the margins of the branches and clavate ends of the 

 ramified peduncles. These pores are, in truth, the commencement 

 of the nutritive system ; they are, in this respect, analogous to the 

 numerous polype-mouths of the compound coral zoophyte ; but in the 

 Rhizostome a common central sac is interposed between the ingestive 

 conduits and the vascular system of the body. Minute animalcules, or 

 the juices of a decomposing and dissolving larger animal, are absorbed 

 by these pores, and are conveyed by the successively uniting oeso- 

 phageal canals to the stomach. Digestion being completed, the chyle 

 passes at once into the vascular system, which is in fact a continua- 

 tion and ramification of the gastric cavity. The nutrient fluid passes 

 by vessels (e), which radiate from that cavity, to a beautiful net- 

 work (/, /) of large capillaries, which is spread upon the under 

 surface of the margin of the disc. The elegance and precision with 

 which the injections of Hunter have demonstrated this network in 

 his preparations cannot be surpassed ; but it is to Cuvier that we owe 

 the first description of the very remarkable and interesting system of 

 nutrition in the Rhizostome.* 



The rich development and reticular disposition of this part of 

 the vascular system, in which the circulating fluids are exposed 

 to the surrounding medium in a state of minute subdivision, upon 

 that surface of the body which rests upon the water, prove that 

 the respiratory interchange of the gases, and the absorption of the 

 oxygen from the air contained in the sea water, take place prin- 

 cipally at this vascular surface of the gelatinous disc; and that 

 Hunter is correct in placing it amongst the series of respiratory 

 organs. It stands, indeed, at the lowest step of that series, since the 

 organ is not specially eliminated, but only indicated or sketched out, 

 as it were, by a modification of part of the common integuments. 



In the CyancBa aurita, another species of our coasts, another 

 modification of the digestive system has been detected. The digestive 

 sac {fig- 53, a) opens immediately upon the under surface of the body 

 by a single four-lipped mouth ; sixteen canals radiate from the central 

 cavity, eight of which (b, b) form, by their ramifications, the systems of 

 nutrient and respiratory capillaries ; whilst the alternate eight terminate 

 without dividing, each by a minute orifice or anus (c) at the margin 

 of the disc. 



* Journal dc Thysiquc, torn, xlix, 1799, p. 436. 



