Dec. 29, 1887] 



NA TURE 



213 



to be extended during next summer, and we shall probably soon 

 have the satisfaction of knowing whether our climate is suitable 

 to its tastes. If so, it will probably obey the mandate of increas- 

 ing and multiplying ; but its tendency will be towards deplenish- 

 ing rather than replenishing the earth. The prospect is not 

 exactly nice, but we may take some comfort from Prof. Riley's 

 expressed opinion that the Hessian fly will not prove a very 

 serious plague to British agriculturists. 

 Downton, December 10. John Wrightson. 



THE REPRODUCTIVE ORGANS OF 

 ALCYONIDIUM GEL A TIN OS UM. 



T N some specimens of the Polyzoon Alcyonidiwn gelatinosum 

 dredged last summer, I noticed that the colony, in place of 

 being nearly homogeneous in colour and semi-translucent, as is 

 usually the case, had a blotched appearance, caused by the 

 presence of a number of small rounded spots of an opaque 

 grayish-white or pale yellow colour. These average about 

 o"5 mm. in diameter, and are scattered irregularly through the 

 colony. On teasing up a small part in sea-water, and on making 

 a few rough sections of the living colony, I found that the 

 opaque spots were cavities filled with fully developed active 

 spermatozoa. No ova were visible in the polypides of any of 

 the parts examined, so these colonies were evidently in the 

 condition of sexually mature males. It at once occurred to me 

 that this species of Alcyonidium might be unisexual — some 

 colonies male and others female — the males being distinguishable 

 when mature by their spotted appearance. The specimens were 

 preserved for future examination. 



On returning to Liverpool, and looking up the literature of the 

 subject, I find that Hincks states (" British Marine Polyzoa," 

 introduction, p. lxxxvi.)that *^ Alcyonidium gelatinosum, accord- 

 ing to Kolliker, is unisexual," and I gather from the context 

 that it is the individual polypides that are unisexual, and not 

 the whole colony, Hincks, however, does not give a reference 

 to any paper by Kolliker, and I have not been able to find in 

 the literature of the Polyzoa, or in the bibliographies I have 

 consulted, any paper of Kolliker's which would be likely to 

 contain observations on the reproduction oi Alcyonidium ; there- 

 fore I am still uncertain how far Kolliker's remark is intended to 

 apply — to the whole colony, or only to the individual polypides. 

 I know of no other investigations on the subject. 



I have now examined a number of thin sections, of both the 

 spotted colonies (including the one formerly dissected) and the 

 usual translucent ones, and I find : — 



(i) In the spotted colonies there are a number of greatly dis- 

 tended polypides, with their coeloms filled with fully developed 

 spermatozoa. There are also a few ordinary large, but not dis- 

 tended, polypides, containing each a few young ova. 



(2) In the ordinary clear colonies there are neither ova nor 

 spermatozoa to be found. 



It is evident, then, that the colony is hermaphrodite, whatever 

 the polypide may be. But it is also evident that the spotted 

 colonies are virtually males. Their spermatozoa are fully 

 developed, while their ova are still quite inimature. Probably, 

 then, Alcyonidium gelatinosum is, like many of the Compound 

 Ascidians, an hermaphrodite in which the reproductive systems 

 arrive at maturity at different times in the life-history. Most of 

 the Compound Ascidians in which I have found this the case are 

 proterogynous (the female organs maturing first), but Alcyo- 

 nidium gelatinosum appears to be proterandrous. If the 

 polypides are unisexual, then the proterandry refers only to the 

 colony as a whole, but it is possible that each polypide may be 

 a proterandrous hermaphrodite, developing ova after it has got 

 rid of the spermatozoa. I hope to investigate this matter further 

 by keeping some colonies alive at the Puffin Island Biological 

 Station, and examining their condition from time to time. 



In Alcyonidium gelatinosum both the ova and the spermatozoa 

 occur in ordinary polypides, and not, as Hincks states is the case in 

 the closely related species A . mytili, in ' ' gonoecia " (cells contain- 

 ing no polypides). In my sections the alimentary canal and 

 tentacles are found cut across here and there in the masses of 

 spermatozoa. The large cavities containing the spermatozoa are 

 evidently ordinary polypides, with the coelom greatly distended. 



W« A, Hkrdman, 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, December 15. — "Note on the Develop- 

 ment of Feeble Currents by purely Physical Action, and on the 

 Oxidation under Voltaic Influences of Metals not ordinarily 

 regarded as spontaneously oxidizable." By Dr. C, R, Alder 

 Wright, F.R.S,, and C. Thompson, F.C.S. 



The authors have noticed that if two or more different kinds 

 of aeration plates be set up on the surface of the fluid contained 

 in a shallow basin in which the oxidizable metal is immersed, 

 and sufficient time be allowed to elapse to enable the films 

 of air attracted to the aeration plates to attain a condition of 

 equilibrium, different constant values are usually obtained for 

 the E.M. F.'s generated by opposing to the oxidizable metal first 

 one and then the other of any given pair of aeration plates, the 

 currents generated being rendered throughout of too small density 

 for " running down " to take place during the observations by 

 interposing a large resistance in the circuit. If when this state 

 of constancy has been attained the two aeration plates be op- 

 posed to each other with a considerable resistance in circuit, a 

 current passes from the one giving the higher value when opposed 

 to the oxidizable plate through the external circuit to the other ; 

 this current at first is of such magnitude as to correspond exactly 

 with the E.M.F. due to the difference between the E.M. F.'s ex- 

 hibited when the two plates respectively are opposed to the 

 oxidizable metal ; but after some time it gradually diminishes ; 

 even after several days, or even weeks, however, it is usually 

 still measurable ; and if a miniature silver voltameter be included 

 in the circuit, in many cases an appreciable amount of crystalline 

 silver is found to be slowly deposited on the negative electrode 

 of the voltameter, which may conveniently be a thin gold wire 

 immersed to a depth of a few millimetres in silver-nitrate solu- 

 tion, a silver plate or wire forming the positive electrode. Various 

 experiments are described in illustration. 



It is obvious that during the passage of a current the dilute 

 sulphuric acid between the two plates must be electrolysed, so 

 that hydrogen would tend to be liberated on the surface of the 

 plate acquiring the higher potential, and oxygen on that of the 

 other ; the hydrogen whilst nascent would necessarily be more or 

 less completely oxidized to water by the oxygen of the film of 

 condensed air ; so that on the whole the net chemical action in 

 the cell itself would be either nil (if all hydrogen were so re- 

 oxidized) or one absorbing heat (if some of the hydrogen escaped 

 oxidation). The oxygen slowly evolved would escape as such, 

 being dissolved by the surrounding fluid. The effect of this 

 should accordingly be that the efficiency of the air-film on the 

 first plate would be more or less depreciated, and that on the 

 second exalted ; in point of fact, if the two aeration plates in such 

 an arrangement which has been generating a current for some 

 time be (by means of an appropriate switch) disconnected from 

 one another and successively opposed to a given oxidizable plate, 

 the one does give a considerably lower and the other usually an 

 appreciably higher value than the constant ones previously ob- 

 tained (before the two aeration plates were directly opposed 

 to one another) on opposing each severally to the oxidizable 

 metal ; whilst on allowing the cell to stand for some time 

 generating no current, the lower value gradually rises and the 

 raised one falls until sensibly the old constant values are again 

 obtained. 



When silver plates are used in conjunction with a fluid capable 

 of dissolving silver oxide (such as dilute sulphuric or acetic acid 

 or ammonia solution), distinctly larger amounts of current are 

 usually developed than with platinum or gold plates, and simul- 

 taneously silver passes into solution, the plate acquiring the 

 lower potential diminishing in weight, and, in short, behaving 

 precisely as though it were an oxidizable metal, such as zinc or 

 copper. Obviously this is due to the circumstance that with 

 silver the ion liberated attacks the metal of the plate acquiring 

 the lower potential ; but the remarkable part of the action 

 IS that this attack is only partial, so that the amount of silver dis- 

 solved is invariably less than that equivalent to the current passing, 

 i.e. less than that deposited in a silver voltameter included in 

 the circuit. 



Various illustrative experiments are described which show that 

 the difference between the silver dissolved and that deposited by 

 the current is relatively much larger with the weakest currents. 



It is obvious that if silver will dissolve in acids, &c,, under 

 the comparatively feeble oxidizing influence of an aeration plate. 



