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NA TURE 



[August 5, 1922 



Letters to the Editor. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of NATURE. No notice is 

 taken of anonymous communications.'] 



The Mode of Feeding of the Jelly-fish, Aurelia 

 aurita, on the Smaller Organisms in the Plankton. 



While engaged in investigations (carried out with 

 the aid of a Government grant) on the oyster beds 

 in the River Blackwater, a jelly-fish (about 8 cms. in 

 diameter) kept as a pet was given large numbers of 

 oyster larva? to see what it would do with them. 

 From the fate of the oyster larvae it was at once seen 

 that the adult jelly-fish, A urelia aurita, feeds definitely 

 and — normally — automatically on smaller plankton 

 organisms in a manner resembling that in which 

 bivalves, some worms, and other animals feed on plank- 

 ton. On adding the oyster larva; to the jar in which the 

 jelly-fish was living, it was observed that the larva; were 

 quickly formed up on the ex-umbrella surface of the 

 jelly-fish in lines embedded in mucus and were also 

 swept on to and retained in quantity on the oral arms. 

 This immediately laised suspicion, and the jelly-fish 

 was thereupon fed at intervals and carefully observed. 1 

 It was found that small plankton organisms of about 

 the size of oyster larvae were collected from the ex- 

 umbrella surface of the jelly-fish and canied, mainly 

 by ciliary action, towards the rim of the umbrella. 

 The rhythmic waves of contraction of the bell or 

 umbrella assist in carrying the strings of collected 

 plankton-food to the edge of the umbrella, whence 

 they are transferred — by a process not yet fully 

 worked out — either to the oral arms or to the under 

 surface of the rim of the umbrella. At the rim of the 

 umbrella in this jelly-fish there is narrow curtain 

 fringe cut normally into 8 segments so that one 

 portion of the fringe lies between two of the marginal 

 sense-organs (tentaculocysts). The fringe therefore 

 resembles that often seen at the rim of a parasol 

 except that it consists normally of 8 segments. The 

 tentacles arise from the edge of the umbrella at the 

 base of and outside this fringe. 



It has thus been seen that by some means — partly 

 by ciliary action and partly by contraction of the 

 bell — a portion or all of the plankton collected on the 

 ex-umbrella surface of the jelly-fish is transferred to 

 the inner or outer sides of these umbrella fringes. 

 Food-particles consisting of the smaller plankton 

 organisms are, however, also collected on the inner 

 surface of the umbrella and apparently also on the 

 bases of the rim tentacles and transported in mucus 

 by ciliary action to the inner side of the fringe at the 

 edge of the umbrella. Plankton is therefore collected 

 by both ex- and sub-umbrella surfaces and probably 

 also on the bases of the rim tentacles and transported 

 thence to the rim fringe. When the plankton reaches 

 the rim fringe it is carried by ciliary action along the 

 base to the middle of each segment of the rim fringe. 

 Thus when an Aurelia has been feeding there are 

 normally 8 blobs of food collected in the middle 

 portions of the 8 rim fringes, which he exactly opposite 

 the straight adradial canals. It is curious that the 

 point at which the blobs of food are constantly 

 collected is not specially differentiated in any way 

 unless it be by the development of an extra pucker 

 in the rim fringe, which permits the accommodation 



1 Gemmill (Proc. Roy. Phys. Soc. Edin., vol. xx. part 5, 1921) records 

 some interesting notes on food-capture and ciliation in the ephyra of the 

 jelly-fish, which are not, however, the same as in the adult, the structure 

 of which is more complex. 



of the food-mass. As and when the blobs of food are 

 collected, it can be observed that the jelly-fish deliber- 

 ately and apparently consciously licks them off by 

 passing over each the separated lips of an oral arm. 

 The cilia on the internal faces of the arm quickly 

 take charge of the food-mass and pass it into the 

 groove made by the infolding of the sides of the oral 

 arm. From the groove in the oral arm the food can 

 be seen to be carried towards the mouth proper and 

 travel by its own channel into the appropriate gastric 

 pouch to be digested. When an Aureha is actually 

 feeding, food can be seen to be passing into the gastric 

 pouches by four main channels. Oyster larvae 

 dropped on to the central region of the arms near the 

 mouth appeared to be greedily accepted, and within 

 a few minutes had passed into the gastral pouches by 

 ciliary action throughone or other of the four main food- 

 channels. There are, however, two subsidiary food- 

 channels to each gastric pouch, so that on occasions 

 three strings of food can be seen passing into one 

 gastric pouch. 



After noticing the way in which this jelly-fish feeds 

 it was realised that the kind of plankton in the sea at 

 a particular moment could be speedily found out by 

 capturing individuals and extracting and examining 

 the collected food - masses from what may now be 

 called the food-pouches on the rim of the umbrella 

 opposite the straight adradial canal. Fortunately 

 it was a simple matter to catch specimens of Aureha 

 recently washed into the oyster pits at high tide. 

 Examination of such food-masses taken direct from 

 the Aureha showed them to consist of the following 

 planktonic organisms : gastropod larvae, of Crepidula 

 and others, oyster larvae (black spat), copepods, 

 various species including Calanus and Harpacticids, 

 Epicaridian larva; in fair quantity, larvae of cirripedes 

 and copepods, Cypris larvae of balanoids, young 

 polychaetes, especially Polydora, a good number of 

 rotifers, algal threads green and brown, in one case 

 with a large colony of vorticellids attached, eggs of 

 polychastes or rotifers, eggs and tadpoles of Ciona 

 and other ascidians, nematode worms, tintinnoids, 

 a number of diatoms of several species, and some 

 sand grains. In one instance an Aurelia was liber- 

 ated for a few minutes in an oyster pit, which con- 

 tained what was practically a good natural culture 

 of the diatom Nitzschia. On examining the food- 

 masses extracted from the food-pouches of this 

 particular jelly-fish a few minutes after immersion 

 in the water, fairly large numbers of the diatoms 

 were found embedded in the mucoid food-mass. 



It is clear, therefore, that Aurelia feeds mainly 

 on what is technically termed medium to coarse 

 plankton, but that it also captures small quantities 

 of the finer plankton. In addition it is well known 

 that larger organisms are taken and eaten, but from 

 the above description it would seem that in the 

 normal habitat of this jelly-fish, plankton organisms 

 of the smaller kind will constitute the main diet. 



From the relatively slight morphological variations 

 which occur in the group to which Aurelia belongs, 

 it would seem highly probable that a similar but 

 probably modified mode of feeding occurs throughout 

 the group. In some members of the group it is well 

 known that young fishes frequently take shelter 

 under the umbrella and often inside the cavities of 

 the jelly-fish with impunity, but hitherto it has been 

 difficult even to guess at a reasonable explanation of 

 the association of a jelly-fish with — what has often 

 been considered legitimate prey — young fishes. The 

 mode of feeding in Aurelia, however, suggests a 

 possible explanation of this phenomenon if, as is 

 very likely, other allied jelly-fishes feed in a similar 

 way. The aggregation of plankton-food in masses 

 provides an excellent opportunity for parasites, as 



NO. 2753, VOL. I IO] 



