Feb. 7, 1878] 



NATURE 



289 



hours, and the latter in twenty-one and a half ; so that 

 the squares of their periodical times are very near in the 

 same proportion with the cubes of their distances from 

 the centre of Mars, which evidently shows them to be 

 governed by the same law of gravitation that influences 

 the other heavenly bodies." This idea of Swift's, which 

 appears to have only recently come to the knowledge of 

 Prof. v. Oppolzer, is so singular a one taken in connection 

 with the facts of the discovery of the satellites of Mars, 

 that it is not surprising the editor of the Astro7iomische 

 Nachiichten should have transferred it to his columns. 

 Possibly the opinion which has prevailed largely amongst 

 astronomers that, if satellites of Mars existed, they must 

 be very small and close to his disc, may have had origi- 

 nally some connection with Swift's fancy. 



BIOLOGICAL NOTES 



Papuan Plants. — In the Appendix to Baron von 

 Mueller's " Descriptive Notes on Papuan Plants," which 

 we have just received we find some interesting additions 

 to orders already considered, and which we have had 

 occasion to refer to before. In Leguminosse, Acacia 

 holosericea is recorded from Geelvink Bay, found by 

 Beccari ; from the Fly River, by D'Albertis ; and Baxter's 

 River, by Reedy. In Myrtaceae are four additions — 

 Tristania i/iacrospcnna, Myrtella beccarii, M, hirsuttcla^ 

 and Bceckea frutescens. A remarkable myrtaceous plant, 

 with the habit of a Psidmin, is stated to be contained in 

 Dr. Beccari's collection, which Baron Mueller thinks is 

 probably referable to the genus Eugenia. The only 

 flower available for examination had eight petals, being 

 double the number of the calyx lobes. Unless this aug- 

 mentation arose from monstrous growth we are reminded 

 that we have here a species abnormal not only in the 

 genus Eugenia (and to which the name of E. pieiopetala 

 might be given), but also in the whole order of Myrtaceae, 

 except Gustavia. From Mount Arfak, at an elevation of 

 about 6,000 feet Dr. Beccari obtained the first epacrideous 

 plant recorded from New Guinea, though in all likeli- 

 hood others will yet be detected in the higher mountain 

 regions. 



Horse-shoe Crabs.— With reference 'to'the fact that 

 large numbers of trilobites are found on their back, and 

 the inference that when living they probably swam in 

 this position, Mr. Alex. Agassiz states {SilHinanrh Jour- 

 nal) that he has for several summers kept young Limuli 

 (horse-shoe crabs) in his jars, and has noticed that besides 

 often swimming on their backs, they will remain in a 

 similar position for hours, perfectly quiet, at the bottom. 

 When they cast their skin it invariably keeps the same 

 attitude on the bottom of the jar. It is not uncommon to 

 find on the shores, where Limuli abounds, hundreds of 

 skins thrown up and left dry by the tide, most of which 

 are turned on their backs. Again, young Limuli generally 

 turn on their back while feeding. Moving at an angle 

 with the bottom, the hind extremity raised, they throw 

 out their feet beyond the anterior edge of the carapace, 

 browsing, as it were, on what they find in their road, and 

 whisking away what they do not need by means of a power- 

 ful current produced by their abdominal appendages. 



Green Alg^e. — Our knowledge of the life-history of 

 those green-coloured algse which seem to possess a 

 true reproductive system, is progressing with rapid strides, 

 and in the Botanische Zeitung for October and November 

 last two most remarkable papers on two well known (so 

 far as external form goes) species have very considerably 

 advanced our knowledge of the group. The earlier in 

 date (October) of these two memoirs is by the well-known 

 botanists Rostafinski and Woronin on Botrydiuni granu- 

 la(um. This alga was described, by Ray nearly 200 years 

 ago, and is probably known to many as growing up in 

 damp clayey spots, and presenting the appearance of bright 



green blobs about the size of large mustard seeds. 

 Common as this plant is, it is only now that after several 

 years' consecutive watching the authors have been able to 

 clear up the mystery of its life, and to determine that the 

 formation of ordinary zoospores can eventuate in the 

 four following ways {a) from the vegetative plant, (b) from 

 an ordinary zoosporangium, {c) from the root-cells, and 

 {d) from a Hypnosporangium : and as still further means 

 of increase we have {e) cell division, (/) formation of 

 spores, and {g) formation of isospores. Botrydium would 

 also seem to enjoy a five-fold resting state : i. The 

 asexual aquatic zoospores with a quiescence of one month. 

 2. The root-cells, quiescence the year through in which 

 they are formed. 3. The hypnosporangia, quiescence 

 the same. 4. The spores, quiescence a year. 5. The iso- 

 spores, quiescence at least over the year in which they 

 were formed. The next memoir is a joint one by A. 

 de Bary, the able editor of the journal, and E. Stras- 

 burger, and is about that very beautiful green sea- 

 weed not uncommon in the Mediterranean, called Aceta- 

 bularia tnediterranea. This genus was so called by 

 Lamouroux on account of the saucer (acetabulum) like 

 form assumed by the little rows of filaments that crown 

 the cylindrical stalks. There are three species known, 

 perhaps they may be all varieties of the one now referred 

 to. Prof, de Bary was only enabled to watch the pro- 

 gress of the spore development to a certain stage, but by 

 Strasburger's researches, carried on at Spezia, we are 

 enabled to read the whole history and to know that the 

 motile bodies of protoplasm set free from a mother-cell. 

 Can and do conjugate, forming a resting body which can 

 and does vegetate. At the close of this memoir Stras- 

 burger proposes that we should call the body formed by 

 the conjugation of the contents of two cells (Gametae) by 

 the name of Zygote, and that those plants whose Gamete 

 are active might be called Planogameta, and those where 

 (as in Desmids) the Gameta are at least quasipassive, 

 might be called Aplanogameta. 



Deep Sea Ascidians.— Mr. H. N. Moseley has pub- 

 lished (Transactions, Linnean Soc. S.S. Zool., vol. r) a 

 description, accompanied by excellent figures, of two very 

 remarkable forms of ascidians. The first described was 

 obtained from the great depth of 2,900 fathoms in the 

 North Pacific Ocean, and is called Hypobythius calycodes 

 in allusion to its occurrence at so vast a depth and to its 

 cup-Uke form. Its outer skin is hyaline and extremely 

 transparent, but in certain places it is strengthened by 

 the presence of tough cartilaginous plates, and these are 

 arranged in a nearly symmetrical manner. It is attached 

 by means of a stalk. It is probably allied to the genus 

 Boltenia, but is abundantly distinct from all known forms. 

 The second is a beautiful stellate form taken 1070 fathoms, 

 not far from one of the Schouten Islands. From its 

 having eight long radiating processes it was at first taken 

 for a medusoid form. Its test is hyaline and gelatinous 

 and it is also an attached form, but the stalk is short. 

 The respiratory sac is flattened out so as to become nearly 

 horizontal, and there is no gill net-work present. It has 

 been called Octacnemus bythius. 



The Bvssus in the Mussel. — Tycho Tulberg has 

 published in the Transactions of the Royal Society of 

 Natural History of Upsala (July, 1877) an account of the 

 structure of the byssus-forming gland in Mytilus edulis. 

 The strong silky threads formed by this gland, which 

 moor the mussel shell so firmly to its resting-place, must 

 be famihar to most. In an allied genus (Pinna) these 

 threads have been even spun and formed into gloves. 

 The manner in which the tongue-like foot can affix these 

 threads is easily to be seen by watching a small specimen 

 of the common mussel when in a healthy condition and 

 confined in a glass jar. The minute structure of the 

 gland that secretes the threads is well described by Mr, 

 Tulberg, who promises further to publish an account of 



