94 



NATURE 



[May 24, 1888 



May 17. — " On the Structure of the Electric Organ of Raia 

 circularise By J- C. Ewart, M.D., Regius Professor of 

 Natural History, University of Edinburgh. Communicated by 

 Prof. J. Burdon Sanderson, F.R.S. 



This paper gives an account of the structure of the cup-shaped 

 bodies, which, as mentioned in a previous paper read on April 26, 

 1888, make up the electric organs of certain members of the 

 skate family. The structure of these electric cups has been 

 already studied in three species of skate, viz. Raia fullonia, R. 

 radiata, and R. circularis. The present paper only deals with the 

 electric organ of R. circularis. It shows that the caps in this species 

 are large, well-defined bodies, each resembling somewhat the cup 

 of the familiar " cup and ball." The cup proper, like the disks 

 of R. Sails, consists of three distinct layers, (1) the lining, which 

 is almost identical with the electric plate of R. batis ; (2) a thick 

 median striated layer ; and (3) an outer or cortical layer. The 

 lining or electric plate is inseparably connected with the terminal 

 branches of the numerous nerve-fibres, which, entering by the 

 wide mouth in front, all but fill the entire cavity of the cup, and 

 ramify over its inner surface, the intervening spaces being 

 occupied by gelatinous tissue. This electric layer, which is 

 richly nucleated, presents nearly as large a surface for the ter- 

 minations of the electric nerves as the electric plate which 

 covers the disk in R. batis and R. clavata. The striated layer, 

 as in R. batis, consists of numerous lamellae, which have an 

 extremely contorted appearance, but it differs from the corre- 

 sponding layer in R. batis, in retaining a few corpuscles. The 

 cortical layer very decidedly differs in appearance from the 

 alveolar layer in R. batis. It is of considerable thickness, con- 

 tains large nuclei, and sometimes has short blunt processes 

 projecting from its outer surface. These short processes ap- 

 parently correspond to the long complex projections which in 

 R. batis give rise to an irregular network, and they seem to 

 indicate that the cortical layer of R. circularis essentially agrees 

 with the alveolar layer of R. batis, differing chiefly in the amount 

 of complexity. Surrounding the cortex there is a thin layer of 

 gelatinous tissue in which capillaries ramify. This tissue evidently 

 represents the thick gelatinous cushion which lies behind the 

 disk in R. batis, and fills up the alveoli. 



The stem of the cup is usually, if not always, longer than the 

 diameter of the cup. It consists of a core of altered muscular 

 substance, which is surrounded by a thick layer of nucleated 

 protoplasm continuous with the cortical layer of the cup, and 

 apparently also identical with it. 



The cups are arranged in oblique rows to form a long, slightly- 

 flattened spindle, which occupies the posterior two-thirds of the 

 tail, being in a skate measuring 27 inches from tip to tip, slightly 

 over 8 inches in length, and nearly a quarter of an inch in width 

 at the widest central portion, but only about 2 lines in thickness. 



The posterior three-fifths of the organ lies immediately beneath 

 the skin, and has in contact with its outer surface the nerve of 

 the lateral line. The anterior two-fifths is surrounded by fibres 

 of the outer caudal muscles. It is pointed out that while the 

 organ in R. circularis is larger than in R. radiata, it is relatively 

 very much smaller than the organ of R. batis. 



Linnean Society, April 19. — Mr. Carruthers, F.R.S. , 

 President, in the chair. — Prof. Martin Duncan exhibited Pa 

 specimen of Heterocen'rotus mamillatus, showing the apertures 

 of three of the genital ducts to be in the median interradial 

 sutures, the corresponding basal plates being imperforate. A 

 discussion followed, in which Mr. W. Percy Sladen and Dr. C. 

 Stewart took part. — Mr. George Murray exhibited some 

 specimens of Spongocladia, with explanatory coloured diagrams, 

 and made some interesting remarks on the presence of sponge- 

 spicules on Algae at present unaccounted for. — Mr. D. Morris, 

 of Kew, exhibited, and made remarks upon, the bird-catching 

 sedge, Uncinia jamakensis. — Mr. John R. Jackson, of Kew, 

 exhibited some table mats from Canada made of the highly 

 scented grass Hierochloa borealis, and a sample of the so-called 

 pine wool prepared from the leaves of the American long-leaved 

 or turpentine-yielding pine, Pinus australis, with a mat made 

 from the wool, an industry which has recently been started, on a 

 large scale at Wilmington, North Carolina. — Mr. J. E. Harting 

 exhibited a living specimen of Natterer's bat, which had been 

 captured the previous day at Christchurch, Hants, together with 

 a water-colour drawing from life of Daubenton's bat recently 

 taken at the same place. — The first paper of the evening was by 

 the Rev. George Post (communicated by Mr. Thiselton Dyer), 

 and contained descriptions of new plants from Palestine. In 

 .the absence of the author, the salient points in the paper were 



admirably demonstrated by Mr. J. G. Baker, F.R.S., who 

 exhibited specimens of the plants alluded to. — A paper was then 

 read by the Botanical Secretary, Mr. B. Daydon Jackson, on 

 behalf of Prof. Fream, on the flora of water meadows. An 

 interesting discussion followed, and the meeting adjourned. 



May 3. — Dr. John Anderson, F.R.S., Vice-President, in 

 the chair. — The Chairman announced a resolution of the 

 Council to found a gold medal, to be called the " Linnean 

 Medal," to be awarded at the forthcoming anniversary 

 meeting to a botanist and zoologist, and in future years 

 to a botanist and zoologist alternately, commencing with a 

 botanist. — Dr. Francis Day exhibited sune specimens of Loch- 

 leven and sea trout raised at Howietoun to illustrate his obser- 

 vation that the markings usually relied upon to distinguish the 

 species are not constant, and therefore, taken alone, of no value 

 for the purpose of identification. He also exhibited specimens 

 of trout from Otago, New Zealand, descendants of some 

 which had been introduced there, presenting some curious modi- 

 fications of structure. A discussion followed, in which some 

 interesting remarks were made by Prof. Howes and Mr. Willis 

 Bund. — On behalf of Mr. Miller Christy, the Botanical 

 Secretary (Mr. B. Daydon Jackson) exhibited some specimens of 

 the Bardfield oxlip {Primula elatior, Jacquin), gathered near 

 Dunmow, and occurring only in this part of England (cf. 

 Trans. Essex Field Club, iii. p. 148). — Mr. A. D. Michael read 

 a paper on the life-histories of the Acari Glyciphagus domesticus 

 and G. spinipes. After describing in detail observations and 

 dissections extending over three years, the author concludes that 

 there is a hypopial stage in the life-history of Glyciphagus, but 

 far less developed than in Tyrogly pints, and not an active stage 

 in the species observed ; that it does not occur to all individuals 

 of a species, and it has not been ascertained whether it occurs in 

 all species ; that the stage is not the result of desiccation or un- 

 favourable conditions ; and that it occupies the period between 

 the penultimate ecdysis and that immediately previous. Dr. C. 

 Stewart criticized Mr. Michael's researches in favourable terms. 

 — A communication was then made by Mr. C. B. Clarke on 

 root-pressure. He contested the view of A. Sachs (and his 

 followers) that root-pressure is sufficient to su-tain the weight of 

 a column of water of the height of 100 (or even 30) feet, and 

 to force out drops at particular points of the leaves. He main- 

 tained that it was a mathematical error to apply the equation 

 p = g/>z to the case of water in plants, and that in a collection 

 of cells and longitudinal tubes of varying size (all very small) 

 the only mechanical ideas that could be applied were those of 

 capillary attraction and motion.. In the discussion which 

 followed, Prof. Marshall Ward thought root-pressure necessary 

 to explain the admitted results of manometer experiments. Mr. 

 A. W. -Bennett, on the other hand, regarded the assumption of a 

 high fluid tension in the cells of roots to drive moisture to the 

 summits as nothing more than an expression of our ignorance 

 as to what the water does move. — A paper on the ovicells of 

 some Lichenoporae was read by the Zoological Secretary (Mr. W. 

 Percy Sladen in the absence of the author, Mr. A. W. Waters. 



k 'Physical Society, April 28. — Prof. Reinold, F.R.S., 

 resident, in the chair. — The following communications were 

 read : — On electromotive force by contact, by Mr. C. V. Burton. 

 The object of the paper is to discuss the seats of the electro- 

 motive forces developed by the contact of conductors. By 

 considering the distribution of electricity on the surfaces of 

 the conductors, and from the fact that the potentials 

 throughout their masses are constant, except about a thin layer 

 near the junction, the author deduces that "the molecular action 

 which gives rise to a contact E.M.F. between t ivo conductors is 

 confined to the immediate neighbourhoo I of the Junction." If 

 E be the contact E. M.F., and M the quantity of electricity which 

 passes across the junction when two metals originally at the 

 same potential are placed in contact, it is shown that the work 

 done is KM, half of which is spent in producing heat and half in 

 raising the potential energy of the system. Since the conductors 

 are supposed to be kept at constant temperature, and the action 

 which gives rise to the E.M.F. is confined to the immediate 

 neighbourhood of the junction, the molecular energy must be 

 absorbed at the junction. By supposing the surface of contact 

 very small, and the capacity of the system large, it is shown 

 that heat and chemical action are the only kinds of energy which 

 fulfil the required conditions of supplying an indefinite amount 

 of energy. Hence, for substances chemically inactive, " the true 

 contact E. M. F. is equal to their coefficient of the Peltier effect 



