326 ORGAN'S OF DIGESTION. 



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conchiferous mollusca. On inverting the disk (D) we 

 observe the short quadrangular oesophagus in the centre, 

 leading to a capacious gastric cavity partially divided into 

 four sacs (C. d.) and from each of these sacs numerous 

 alimentary canals (D. q. q. q. g) radiate towards the mar- 

 gin of the mantle, ramifying with great regularity, but pre- 

 senting few anastomoses compared with those of the rhizos- 

 tomes. Around the lower part of the stomach are disposed 

 the four ovarial sacs (D. e. e e. e) containing the coloured 

 ovaries, and opening externally each by a distinct aperture 

 as in other medusae. The inner surface of the stomach has 

 a spotted follicular appearance, and this divided cavity is 

 separated by a double membrane from the open ovarial sacs 

 beneath. From around the margin of the stomach there 

 come off sixteen canals, alternately simple and ramified, which 

 end in the circular vessel (D. r. r.) passing round the mar- 

 gin, and by placing the living medusa in sea water tinged 

 with indigo, the stomach (C. d.) the radiating vessels (D. g. 

 g. g. g.) and the circular marginal canal (D. r. r.) are soon 

 found filled with the blue coloured infusion while the rest 

 of the animal remains colourless. A nervous circle is seen 

 around the oral passage from which the long tentacula (C. D. 

 p. p.) are suspended; another nervous cord accompanies 

 the circular canal (D. r. r) around the free margin of the 

 mantle which is fringed with a row T of minute tentacula (D. 

 o.o.) highly sensitive and in constant motion ; the organs of 

 vision (D. n. n.) are placed in the sight depressions around 

 the free edge of the disk ; and in the middle of each of the 

 eight lobes of the mantle, between each pair of eyes, is 

 seen the dilated anal termination of a simple excrementitious 

 canal (C. D. o. o. o. o.) generally containing the indigesti- 

 ble remains of very minute articulated and molluscous ani 

 mals, which are thrown out by these eight marginal ani on 

 alarming the medusa. Currents of digested matter are seen 

 moving through the radiating ciliated canals of medusae, as 

 in those of the ciliograde acalepha and the corresponding 

 organs of other radiated classes. In the carybdea marsupia- 

 lis, which was thought to be agastric, there is a central infe- 

 rior oral aperture, surrounded by four short conical tentacu- 

 la, the stomach is partially divided into four compartments, 

 from each of which a canal extends to the free margin of the 



