278 



HARD WICKE'S S CI EN CE- G O SSI P. 



and consists of five antimera or parts ; it forms a true 

 stock or cormus, which is composed of five articu- 

 lated, worm-like, bilateral persons. When this 

 cormus originates within the nurse by budding, a 

 multiplication of antimera occurs, whereby from one 

 antimera five arise. This origin can be interpreted 

 only as a non-sexual reproduction, not as a mere 

 transformation. The true nature of these genuine 

 alternate generations is clearly shown by those sea- 

 stars, in which the body remains free from the five 

 (or more) independent arms, and the central disk, 

 which barely unites the latter in the middle, exists 

 almost as an independent body. These are Ophidi- 

 aster, ChtTtaster, Brisinga, &c. Particularly inte- 

 resting in this relation are most species of the genus 

 OpJiidiaster, or Linckia, from which several specimens 

 are exhibited (0. diplax, O. ornithopus, O. multi- 

 formis, and 0. Ehrenbergii). Here the single arm, 

 which possesses the morphological value of an 

 articulate worm, is freely detached from the disk, and 

 every arm forms by regeneration both the central 

 disk and the four remaining arms. With numerous 

 specimens of the four species of Ophidiaster selected, 

 all the various stages of this reproduction process 

 were shown, and he discussed the significance which 

 these so-called comet forms of sea-stars possess for 

 the morphological interpretation of the same. There- 

 fore we should take as the oldest stem form of the 

 Echinodermata the Asteroidea, from which as di- 

 verging branches have developed Ophipridea, Crinoi- 

 dea, and Echiuoidea. In the last, the centralization 

 of the whole cormus is carried farthest, and from 

 them the Holothuroidea have arisen. Thus the Holo- 

 thuroidea stand most distant from the original form 

 of the Echinodermata — the Asteroidea." 



BOTANY, 



Cotoneaster vulgaris.— This plant still exists 

 in small quantities on the Orme's Head. I saw it 

 there in July last. — James Brittot. 



Polypogon Littoralis.— This rare plant, which 

 does not appear to have been recorded for Glouces- 

 tershire, occurred this year in considerable quantity, 

 on marshy ground, near the north bank of the Avon 

 river at Bristol. On inquiry it seems that the soil 

 here has been taken from the river bank and bed 

 at places much nearer Clifton, when the river was 

 widened and the new dock-gates constructed, and 

 brought to this marsh to fill hollows from which the 

 clay had been dug for manufacturing purposes. Its 

 appearance is of interest, as furnishing another instance 

 of the occurrence of new plants when soil that has 

 been long buried is brought to the surface. 



Lizard Orchis [Orchis kircina).—! had sent 

 to me last June a very fine specimen of the Lizard 

 Orchis {Orchis hircind). It was found in a chalk- 



pit at Greenhithe. As I see from Hooker and 

 Arnott's "British Flora," published 1850, that the 

 plant " is very rare (perhaps now extinct)," it maybe 

 interesting to your readers to know it has been found 

 so recently. I enclose one dried blossom that you 

 may be sure of its authenticity. The plant was nearly 

 3 ft. high, the spike of blossom over 21 in. Per- 

 haps if it has been found by any other of your 

 readers they will let you know, as it must be a plea- 

 sure to know so handsome a plant is not yet extinct. 



GEOLOGY, 



A New Genus of Fossil Corals. — Mr. James 

 Thomson, F.G.S., who is well and widely known as 

 an enthusiastic student of carboniferous corals, has 

 just published a monogram on a new genus, which he 

 has named Albertia. He also gives us, in the same 

 elaborate paper, a short sketch by which it has been 

 attempted to delineate the internal structure of fossil 

 carboniferous corals during the last twenty years. 

 Most palaeontologists are aware that Mr. Thomson 

 has succeeded in causing thin sections of coral to 

 photograph themselves on sensitised copper-plates, 

 so that every line is truthfully portrayed. Mr. 

 Thomson, after a long account of failures that would 

 have damped the ardour of a less enthusiastic geolo- 

 gist, relates his triumph as follows : — "It would be 

 tedious to enumerate the various other unsuccessful 

 attempts I made in the way of obtaining casts fitted 

 for the accurate reproduction of structural details ; 

 but I may say, generally, that these attempts were 

 veiy numerous, that they occupied a large portion of 

 my leisure time for several years, and that they in- 

 volved a very considerable amount of expense. Out 

 of these laborious attempts, however, there finally 

 emerged the process which I now employ, and for 

 which I claim the merit of being applicable to the 

 accurate delineation of the minutest details of coral- 

 line structure, and of being comparatively inexpen- 

 sive. This process I have now used for two years for 

 the production of lithographic plates, and quite re- 

 cently I have succeeded in modifying it so as to pro- 

 duce electrotypes for use in the ordinary printing- 

 press. Of the first form of this process, I may say 

 that it consists in taking an impression of the struc- 

 ture upon a sensitised copper-plate, that this impres- 

 sion is then engraved upon the plate, and that a 

 transfer is thence taken and put upon a lithographic 

 stone. Of the second form of it, I may say that an 

 impression is taken upon a plate of sensitised copper, 

 that the plate is next engraved and etched very 

 slowly, but somewhat more deeply than in the first 

 case, that a cast in wax is taken from the plate, and 

 that from this again is produced an electrotype in the 

 ordinary way. The fact that the process which I 

 have now so far described is applicable not merely to 

 the delineation of structures presented in my own 



