288 



NA TURE 



\_Feb. 7, 1878 



permanent fin appears like a second anal fin, the resem- 

 bUnce to the tail of a young Lepidosteus is most striking. 

 The extremity of the notochord at last disappears pre- 

 paratory to the formation of the urostyle, while the 

 permanent caudal gradually develops/ and soon it (Fig. 3) 

 presents the general outline of the adult form. 



A. Agassiz has traced the presence of this remarkable 

 embryonic caudal-lobe in a large number of genera of 

 bony fish. In the young of Syngnathus it is well marked. 

 In the young of the fishing- frog (Fig. 4) {Lophius) the 

 termination of the notochord remains unchanged quite 

 late in life, but in all the genera examined the permanent 

 tail passes quite gradually from a strictly ventral ap- 

 pendage placed below the dorsal column to that of a 

 terminal tail placed in the continuation of the vertebral 

 column. 



A. Agassiz thinks that though Agassiz and Vogt were 

 mistaken as to their details, their great generalisation will 

 still remain true, and that there is a complete accordance 

 between the embryonic growth of fishes' tails and the 

 development of fishes in time, only we must now remem- 

 ber that the heterocercal tail is not the earliest stage — 

 that the earliest stage is a nearly symmetrical one ; this 

 ■which he calls the leptocardial stage is that assumed by 

 the tails of bony as well as of all. other fishes, a.nd precedes 

 the heterocercal stage. As to the.palseontological record, if 

 one examines the tails of the Devonian fish as we know 

 them from the restorations of Agassiz, Hugh Miller, 

 Hsckel, Huxley,] and others, one is quite struck by the 

 .perfect parallelism of these ancient fishes, as far as the 

 structure of their tail is concerned, with the structure of 

 the stages of the flounder's tail already referred to, thus 

 carrying out the. parallelism of Agassiz and Vogt far beyond 

 anything they even conjectured. This important paper 

 of A. Agassiz was presented to the American Academy 

 of Arts and Sciences in October last, and for an early 

 copy of it we are indebted to the author. 



E. Perceval WrighiT 



OUR ASTRONOMICAL COLUMN 



Literature of the Nebula and Clusters. — No. 

 311 of the Smithsonian Miscellaneous Collections is just 

 received. It contains an " Index Catalogue of Books and 

 Memoirs relating to the Nebulae and Clusters, &c.," by 

 Prof. Holden, of Washington, commenced in 1874 for his 

 own use, and now published in the hope, as he states, 

 that it may be found as useful to others as it has already 

 been to himself. It is believed to be nearly complete so 

 far as the uses of the astronomer can require, but it has 

 not been Prof. Holden's object to make an index for the 

 bibliographer. The present catalogue affords facilities in 

 the several cases that are most likely to arise, as first, in 

 the event of all that is published on nebulas and clusters 

 in a particular series — the Philosophical Transactions, 

 for instance — being required ; again, where all papers 

 <upon the subject by any one author are sought for, and 

 further, when all papers written upon any special subject, 

 no matter by what author, are in question. A very useful 

 indication of the contents of a large number of the 

 memoirs and notices forms a feature in the work, Sir W. 

 Herschel's papers being' noticed in abstract with par- 

 ticular fulness. The great nebula in Orion and the 

 variable nebulas claim separate sections. There are also 

 lists of figured nebulas and an index to Sir W. Herschel's 

 Catalogues adopting the identifications of his son's 

 General Catalogue. 



Prof. Holden has rendered an essential service to all 

 who may be occupied with this interesting branch of 

 astronomy, who will find his index of the greatest assist- 

 ance in enabling them to learn, at the expense compara- 

 tively of little time and trouble, all that has been written 

 upon many special subjects and upon the nebulae and 

 clusters geneially. 



New Southern Variable Star. — Mr. Tebbutt— who, 

 it will be remembered, was the discoverer of the great 

 comet of 1 861 while yet telescopic — writing from Windsor, 

 New South Wales, on November 23, notifies his having 

 detected what would appear to be a remarkable variable 

 star in the constellation Ara. He had seen it as a star of 

 the fifth magnitude while observing Comet III., 1863, 

 between October 3 and 9 ; it was then brighter than o- 

 Aras, and plainly visible to the naked eye. Its place was 

 fixed by sextant-distances from four stars. At the time 

 of writing, Mr. Tebbutt mentions that the only star in 

 the observed position was one of the eleventh magnitude, 

 barely distinguishable in moonlight in his 45^-inch equa- 

 torial When this star was placed in the centre of a field 

 of about 45', no stars above the tenth magnitude were 

 visible. But, in this case, what has become of No. 6142 

 of the Paramatta Catalogue, rated 7 '8 m. ? Mr. Tebbutt 

 found the place of his star for 18780, R.A. I7h. 30m. 135*2, 

 N P.D. 135° 24' 17", in which case Brisbane's star would 

 be distant i6'"8 on an angle of 193°, and should therefore 

 have been in the field. 



While writing on the subject of variable stars, we may 

 mention that the Annuaire dti Bureau des Longitudes for 

 1878 contains very full lists and ephemerides of these 

 objects, which have been ably prepared from Prof. Schon- 

 feld's catalogue and other sources by M. Lcewy, who now 

 has charge of the popular French work. In other respects 

 the Annuaire for the present year is to be recommended 

 as a valuable repertory of scientific facts and data. 



The Royal Observatory, Brussels. — M. Houzeau, 

 the successor of the late M. Quetelet in the direction of 

 this establishment, has issued his report on the work of 

 the year 1877. The Observatory is at present in a tran- 

 sition state, the instruments which have long been in 

 use being about to be replaced by others of greater 

 capacity. A meridian circle, almost entirely similar to 

 that constructed for the new Observatory at Strasburg, 

 has been ordered from Repsold ; and Dent, of London, 

 supplies the standard sidereal clock, to be accompanied 

 by a chronograph : various modifications have been 

 introduced into these instruments after careful con- 

 sideration. A refractor of 38 centimetres aperture is in 

 course of construction by Merz, the object-glass having 

 already arrived at Brussels. The ancient meridian 

 instruments have been employed on the observation of 

 stars exhibiting decided proper motion, a work long 

 pursued. On the mounting of the large refractor, M. 

 Houzeau proposes to fix his attention upon three prin- 

 cipal objects : — ist. Micrometrical measures of a certain 

 number of double stars — binaries, and those which are 

 affected with rapid proper motion. 2nd. To observe, 

 with particular care, the passages of the satellites of 

 Jupiter across his disc, and their occultations and the 

 transits of their shadows. 3rd. Spectroscopic obser- 

 vations, for which a smaller refractor will also be avail- 

 able. Meteorological observations which have occupied 

 much of the time of the observers during M. Quetelet's 

 superintendence, will be continued, but in a department 

 distinct from that devoted to astronomy, a very necessary 

 arrangement if observations of a routine nature are not 

 to be allowed to interfere with those of a higher class. 



A Forecast of the Satellites of Mars. — In the 

 last number of the Astronomische Nachrichten, Prof, von 

 Oppolzer, of Vienna, draws attention to the curious 

 passage in the " Travels into Several Remote Nations of the 

 World by Lemuel Gulliver^' — of Swift, which he transcribes 

 from the edition of 1755. A correspondent of the Times 

 referred to the same passage soon after the discovery of 

 the satellites of Mars by Prof. Asaph Hall became known 

 in this country. We read " they have likewise discovered 

 two lesser stars or satellites which revolve about Mars, 

 whereof the innermost is distant from the centre of the 

 primary planet exactly three of his diameters, and the 

 outermost five \ the former revolves in the space of ten 



