42 ACALEPH^E. 



The mouth is large, the oesophagus straight and would form so many openings into this cavity 

 wide; the stomach is, for the most part^ of an were they not closed by a fine and plaited 

 ovate form, the intestine passes in a straight membrane, which bulges outwards when the 

 line, and with a uniform diameter, to its ex- stomach is filled. From the circumference of 

 tremity. The anus has a prominent circular the stomach, at equal distances, sixteen vessels 

 margin in cydippe. No absorbent vessels can arise, and run directly towards the margin of the 

 be seen arising from the gastric cavity. In disc. These vessels may be regarded as arteries, 

 many species, the alimentary canal is so large and will be hereafter described along with other 

 as to occupy the greater part of the interior of structures more nearly resembling the parts of 

 the body. When there is no food within it, it a circulating system. ButCuvier* was disposed 

 remains open at both extremities, and, as the to consider them as cceca; although he ad- 

 animal swims generally with its mouth fore- mitted that he could discover no other vessels 

 most, there is a current of water continually fitted to discharge the functions of arteries, 

 passing through it. Eschscholtz observed, that He remarked that if we regard them as arteries, 

 when suitable aliment was carried by this cur- we must look upon the little vessels which lead 

 rent against the walls of the stomach, the from the appendages or arms to the central 

 orifices were immediately contracted, and the cavity, as veins, or as lymphatics; and then 

 digestive process begun. Minute Crustacea, we might say that the sea is as a stomach 

 salpae, &c., have been found in the stomachs to the rhizostoma, in the same way as the 

 of ciliograda. The diligent observer just men- earth acts as a stomach for plants. But, at all 

 tioned seemed to regard the canal leading from events, Cuvier was convinced by his dis- 

 the stomach to the dorsal surface, (which we sections that alimentary matter enters the body 

 have called the intestine,) as forming no part of through the marginal oscules of the arms, 

 the digestive organs. He termed it " the and that it is accumulated in the internal cavity 

 water-canal," and considered it as connected before passing into the radiating vessels. 

 merely with the peculiar mode of locomotion, By experiments on the living animal, Dr. 

 inasmuch as he observed it so patent while the Milne Edwards has recently provedf that the 

 animal was swimming and not digesting as to circumambient fluid and its contents of mi- 

 admit of a free passage for the water; which, nute size do really enter the body of the 

 otherwise, in entering the open mouth, would rhizostoma through the margins of the arms, 

 have much impeded progressive motion. He placed a living rhizostoma in sea-water, 

 It was generally believed, until within a very artificially coloured red. The animal did not 

 recent period, that some of the pulmograda appear to suffer from the presence of the 

 were destitute of stomachs. Hence the term colouring matter. Within a very short time, 

 of agastric medusa which was applied to them the puckered membrane which borders the 

 by Peron. The researches of Dr. Milne Ed- arms was distinctly tinged red, and, gradually, 

 wards, however, have rendered it probable that the colour ascended, until the whole body 

 this supposition was erroneous, and founded assumed the same tint. Dr. Edwards does not 

 on inaccurate observations. We have nowrea- state, however, whether he traced the progress 

 son to believe that all the pulmograda have of the coloured fluid through the brachial 

 gastric cavities ; but all have not true mouths, canals and the vascular system. On placing 

 There are some in which the only communica- the same individual again in pure sea-water, 

 tion between the stomach and the outer surface the colouring matter which had been absorbed 

 is through numerous ramified canals in the disappeared gradually, and it seemed to Dr. E. 

 pendent arms, which open externally by ex- that it was thrown out chiefly from the brachial 

 tremely minute orifices, barely sufficient, even fringes, but partly also from the margin of the 

 in large species, to admit the smaller ento- disc, and from the capillary orifices situated at 

 mostraca. Such a structure exists in rhizostoma. the extremities of the arms. Dr. Edwards 

 By injecting milk into its gastric cavity, the satisfied himself that it is impossible for ani- 

 canals in its arms, and their oscules can be mals larger than small animalcules to enter the 

 rendered visible ; and it is then discovered central cavity of the rhizostoma. But most of 

 that from the minute oscules, which are situ- the pulmograda have large central mouths, 

 ated in indentations along the margins of the either simple and sessile, or placed at the ex- 

 arms, small vessels proceed inwards, > and, tremity of a projection from the lower surface 

 uniting in twos and threes together, open into of the disc. In some, the mouth is more or 

 one large canal which runs through the middle less patent, but capable of being closed by the 

 of each arm. These arms are large, fleshy, approximation of the base of the arms. In 

 foliated organs, eight in number ; each of which others it is surrounded by a ring of conside- 

 has a triangular shape. The eight canals above rable density, in which muscular fibres can be 

 mentioned unite two and two, so as to form distinctly seen. In medusa aurita, there are, 

 four great trunks, which open into a large just within the cavity of the mouth, four open- 

 central cavity, the only one in the body, ings, which lead, by as many short but wide 

 This cavity is situated at the base of the central canals, into four spherical sacs of considerable 

 process pendent from the lower surface of the size. These are completely separated from 

 disc. The base, in rising upwards, enlarges one another by membranous partitions. That 

 into four fleshy columns, which lose them- they are stomachs is proved by the circum- 

 selves in the disc. It is between these four 



fleshy columns that the cavity of the stomach is * Journ. de Phvs. xlix. 438 



placed. The intervals between the columns t Ann. des Sc. Nat. xxviii. 24!). 



