ORGANS OF DIGESTION. .32.1 



succeeded by a gastric expansion of this straight canal, contain- 

 ing frequently minute entomostracous Crustacea which have 

 been swallowed as food, and a narrow straight intestine ter- 

 minates in a prominent anal orifice at the upper part of the 

 body. The numerous ciliated canals conveying currents and 

 globules through every part of the animal appear to be 

 connected with the alimentary cavity, as in zoophytes and 

 in other acalepha, and currents of water appear to flow 

 through the alimentary canal in its empty state. In the 

 aldnoe vermiculata, provided also with eight longitudinal 

 bands of vibratile cilia, the alimentary canal passes straight 

 through the axis of the body, surrounded below, at its oral 

 entrance, as in beroe, with four prolonged marginal lips, 

 but here of a lengthened conical form like the tentacula of 

 polypi. Numerous coecal prolongations from the cavity of the 

 stomach are seen in physalia extending into the abdomen and 

 are generally found to contain portions of the digested food. 

 The digestive sacs of the physophora resemble the polypi of 

 companularia, but destitute of tentacula, and their contrac- 

 tions are seen to aid the progressive motions of the animal in 

 floating through the water, as the contractions of medusa 

 and of some heroes assist in their progression. The wide 

 tubular proboscis in the centre of the lower surface of the 

 velella (Fig. 6. 1.) leads to a capacious stomach occupying 

 the middle part of the body, from which minute orifices 

 appear to extend to the numerous small tubular suckers 

 placed around the mouth ; and the same structure is seen in 

 the porpita where the digestive cavity, the only important 

 system yet developed, is protected above, as in velella, by 

 the firm internal skeleton. Around the delicate margin of 

 the berenice, which was thought to be agastric, there are 

 numerous prominent papillae, the tubular passages of which 

 lead to a wide central stomach. Most of the small physo- 

 grade acalepha, as well as the larger pulmodrade medusaria, 

 like inverted zoophytes torn from their fixed attachment and 

 floating through the sea with their polypi extended in all 

 directions, have numerous small pendent orifices at the 

 extremities of peduncles more or less ramified and extended, 

 and these polypiform mouths lead by narrow canals to 

 a central sac, from which the nutritious matter is sent by 

 numerous radiating ramified ducts to all parts of the body. 



