270 



circulating fluids in these animals as the great agent both in the ab- 

 sorption and the growth of parts, and throws out the suggestion, 

 that as it flows into the stomach, it may also act as a solvent to the 

 food received into that cavity. The particles which exist in these fluids 

 show their analogy to those in the blood of the higher animals on the 

 one hand, and to those in the sap of vegetables on the other : some 

 appear to be derived from the digested food, and others from the melt- 

 ing down of parts absorbed. In these polypi the author never saw the 

 least appearance of cilia, or of currents in the surrounding water, 

 which are so frequently met with in other tribes of zoophytes. 



The latter part of the paper is occupied by the account which the 

 author gives of his various observations, first, on Ascidice, of which he 

 enters into an anatomical description ; secondly, on the internal cur- 

 rents of water, permeating the branchial sacs, and determined by the 

 vibratory movements of cilia which are seen in that animal ; and, 

 thirdly, on the alternations in the course of the circulation of the 

 blood in the vessels, which at one time flows in one direction, and, 

 after a certain interval, takes the contrary course ; so that the same 

 vessel which at one time performs the function of an artery, performs, 

 at another, that of a vein. This phenomenon of alternate currents, 

 like that in the Sertularia, was met with in every specimen of Ascidice 

 which was examined by the author, and also in a Polyclinium. 



The paper concludes with several observations on Flustra, from 

 which, as far as relates to the circulation of currents, the author was 

 led to results in many respects analogous to the preceding. 



A paper was then read, entitled, "On the Theory of the Moon." 

 By J. W. Lubbock, Esq., V.P. and Treasurer of the Royal Society. 



The author, adverting to the appearance of M. Plana's admirable 

 work entitled Theorie du Mouvement de la Lune, enters into a com- 

 parison of the analytical methods employed by that author and M. 

 Damoiseau, and points out some differences in the numerical values 

 of the coefficients of some of the arguments in the expression for the 

 true longitude of the moon in terms of her mean longitude. He then 

 prosecutes the subject by a series of analytical investigations, which 

 are not susceptible of abridgement, but from which he obtains formulae 

 which do not quite agree with those of M. Plana. 



A paper was also read, entitled, " Some Suggestions relative to the 

 best method of employing the new Zenith Telescope lately erected at 

 the Royal Observatory." By John Pond, Esq., F.R.S., Astronomer 

 Royal. 



During the observations made by the author, in the course of last 

 summer, with the new zenith telescope lately erected at the Royal 

 Observatory, for the purpose of measuring the zenith distance of 

 y Draconis, it occurred to the author to avail himself of subsidiary 

 observations on another star, of about the fifth magnitude, which has 

 nearly the same zenith distance towards the south that y Draconis 

 has towards the north, and which passes the meridian between 20 

 and 30 minutes, in time, after it. The angular distance between the 



