122 



MARINE AND FISHERIES 



6-7 EDWARD VII., A. 1907 



(i.e. 3 '6 per cent) of sodium chloride, it rythmically contracted for an hour or more. 

 He decided that the ma,rgin differed from the centre of the disc in that species, and 

 contained sodium, calcium and potassium ions in different proportions. The pulsations 

 in the case of Aurelia did not cease after its margin had been cut off. Dr. Macallum 

 found, however, that the contractions of the disc of Aurelia were rare and feeble in 

 ordinary sea-water, after cutting away the margin of the disc, though very vigorous 

 in the § normal solution of chloride of sodium; but he concluded that the salts 

 did not act directly on the tissues, e.g., the nerve cells, muscles, &c., as Dr. Loeb 

 thought; but on the nerve endings in the epithelium of the lower surface of the jelly- 

 fish, usually called the sub-umbrella. This was clear from the fact that all contractions 

 ceased when a 0 "08 per cent solution of formalin in sea-water was gently brushed over 

 the surface, or when the surface was so stroked with the back edge of a scalpel as to 

 scl^pe the epithelium. These ectodermal cells, or epithelium elements, which form 

 the thin covering over the gelatinous bell (mesogloea) possess no markedly contractile 

 character, and have assumed, in the morphologist's view, a function practically 

 sensitive and protective alone, ' they have largely given up,' as the late Professor T. 

 Jeffery Parker said, ' the function of contractility to the muscle processes or fibres.' 

 This layer of living ectoderm prevents that direct influence, and interchange, which 

 Professor Loeb regards as exercised by the chemical environment of the medusae. Any 

 rapid exchange between the outside medium and the salts in the tissues of the jelly-fish 

 is barred, otherwise the composition of the ' jelly,' which forms so large a portion of 

 the disc, would change with every change in the sea-water in which the creature floats, 

 e.g., in passing from ocean water to brackish, and vice versa. 



The gelatinous tissue or jelly is really a supporting lamella between the endoderm 

 and ectoderm layers, but immensely thickened, as compared with the mesogloeal lamella 

 in Hydra, and it is very effective in impeding the exchange referred to, and indeed, in 

 preventing the diffusion of foreign matters. Methylene blue, injected by a hypodermic 

 needle into a vigorously pulsating Aurelia, was found to stain one spot only, and it was 

 not possible to detect any spreading-out of the colour even after 24 hours interval. 

 While the prevention of the diffusion of foreign substances is secured on the one hand, 

 and the retention, on the other hand, is ensured of fluid and inorganic matters, the loss 

 due to injury is also minimized and repairs to the surface are facilitated, even when 

 sucn injuries are extensive. Thus, a third of the disc may be removed ; but the naked 

 cut surface is soon overgrown by a cuticle of small and glistening epithelium cells. 

 The jelly consists of a minutely reticulated meshwork of proteid, called discin, which 

 retains water and inorganic salts, and by its excessive firmness resists diffusion and 

 osmosis so long as the trabeculse are m-.aintained. Though the epithelial cuticle inter- 

 poses a barrier against rapid exchange between the watery environment and the disc 

 substance, and the mesogloea itself resists the diffusion of foreign matters, yet the 

 epithelial cells of the surface of the bell, and the lining cells of the gastro-vascular 

 canals, exercise a remarkable selective power. They take in §ome chemical matters and 

 reject others in the most unmistakabJe manner. 



Before referring to the details of this interesting selective action of the cells as 

 living units, and to the methods adopted by Professor Macallum in his researches, it 

 may be necessary to point out that the composition of medusiB has engaged many 

 observers. Krukenberg found in Rhizostoma .Cuvieri, from the Adriatic, that the solids 

 were 4*608 per cent and the organic 3 per cent; in Aurelia the solids were 4*2056 and 

 4*66 per cent, and in Chrysaora hyoscella, the percentages of solids were 4*25 and 3*7. 

 Ladenburg found in two examples of Aurelia aurita from the Bay of Kiel, where the 

 surface salinity is 1 -7 to 1 '8 per cent on the average, that the solids were 2 '06 in one 

 example, and in another 2 *! per cent. Krukenberg also attempted the estimation of 

 the chlorine in medusae from different localities, and found that Aurelia from east of 

 the mouth of the Ehone showed 1*5975, and Rhizostoma Ouvieri showed 1*65075 per 

 cent, as compared with specimens of Afurelia from the Gulf of Trieste and the Red Sea, 

 which showed a percentage of chlorine as follows : 1 '79275, 2 *0306 and 2 -2223, when 



