4i8 



NATURE 



[March 6, 1890 



"scarcely recognizable" appearance of the crab Ilyas when 

 covered with algse, &c. Indeed, no one who has seen one of these 

 crabs brought up with the dredge, or has found a well-covered 

 Stcnorhynchus on our own shores, can seriously doubt the useful- 

 ness of the habit in rendering the animal inconspicuous. In 

 Stenoj-hynchus and Iiiachus the process of "dressing" with 

 weeds and zoophytes has been described by Bateson (Journ. 

 Mar. Biol. Association, vol. i. 1889, p. 213), and it is seen from 

 his description that, as also in the cases of Dorippe, Pagurus, 

 Di-otnia vulgaris, &c., the foreign substances or animals become 

 attached to the body not by accident but by the act of the crabs 

 themselves. 



Now Mr. Walker, in regarding all these cases as instances of 

 adaptation for concealment, has overlooked the fact that in two 

 of our British species of hermit crab {^Pagurus bernhardtis and 

 P. prideauxii) it is the habit of the animals to prefer, and often 

 to fight for, shells which are rendered conspicuous by the attach- 

 ment to them of species of Anemone, in the one case Adumsia 

 rondeletii (Sagartia parasitica), in the other Adajttsia palliata. 

 Another British species {Pagurus cuanensis) is almost invariably 

 found inhabiting a shell enveloped in the sponge Suberites 

 domuncula, which is frequently of a conspicuous orange-red 

 colour Only in the smallest species of Pagurus {e.g., P. lavis) 

 does the animal depend invariably upon an inconspicuous ap- 

 pearance for its safety. 



The value to the crabs of a preference for shells to which 

 Actinians are attached is found in the fact that these gaily- 

 coloured animals are carefully shunned by fishes on account of 

 their stinging powers ; and although hermit crabs themselves 

 are very palatable to fishes, their association with Actinians, 

 while rendering them conspicuous as they move about, is at the 

 same time an efficient protection from the persecution of their 

 enemies. 



This also explains the habits of the two Mauritian crabs, 

 which, according to Mobius, carry about a sea-anemone in each 

 claw. 



The sponge with which Pagurus cuanensis is associated is (like 

 all other sponges with which I have experimented) exceedingly 

 obnoxious to fishes on account of its bad smell and taste. I 

 have never succeeded in inducing a fish of any species to swallow 

 a fragment of the sponge ; but on the contrary the smell is in 

 most cases quite sufficient to drive the fish away. The associa- 

 tion with the sponge is therefore here also an efficient protection, 

 for I know of no fish capable of extracting the crab from its 

 retreat. It is seen from this that the case of Dromia vulgaris 

 should probably be removed from the category of adaptations for 

 concealment, and, like the cases of P. bernhardus, &c., be in- 

 cluded in a special group of warning adaptations. 



There yet remains the interesting case, adduced by Dr. R. von 

 Lendenfeld, of Drofjiia excavata associated with a Compound 

 Ascidian of the genus Atopogaster {\\&xdsa2,Ti). This, I believe, 

 will be found to belong to the same category of warning adapta- 

 tions, for after repeated experiments with Compound and other 

 Tunicata at the Plymouth Laboratory I can state that these 

 animals are essentially inedible to fishes. The inedibility is in 

 large part due, as in the case of sponges, to the characteristic 

 odour which Tunicata, and more especially Compound Tunicata, 

 give out, and in no family (excepting perhaps the BotryUida;) 

 is this better marked than in the Polyclinida, the group to which 

 Atopogaster belongs. Bearing in mmd also the fact that Com- 

 posite Ascidians frequently vie with sponges and Actinians in the 

 possession of varied and conspicuous colours, it is rendered 

 practically certain that the case of Dromia excavata is another 

 instance of this same type of adventitious warning contrivances. 



Thus the edible (the edibility is not yet proved for foreign 

 species) Crusacea which attach foreign substances to their bodies 

 may be divided into two groups : — 



(a) Those which are rendered inconspicuous in relation to their 

 natural surroundings by the habit ; e.g. , Stenorhynchus, Ilyas, 

 Dorippe, Pagurus Levis, and young forms of Pagurus bernhardus, 

 &c. 



(;8) Those which associate themselves with animals, easily 

 recognizable by, and possessing qualities offensive to, their chief 

 enemies ; e.g., Dromia vulgaris and excavata, Pagurus bern- 

 hardus, prideauxii, and cuanensis. Walter Garstang. 



Laboratory of the Marine Biological Association, 

 Plymouth, February 21. 



P.S. — From facts which Mr. Weldon and Mr. Harmer have 

 communicated to me, it would appear that Dromia vulgaris fre- 

 quently attaches Compound Ascidians {Leptoclinum maculosum. 



Botrylloides Gasconice) to its back instead of sponges, a variation 

 of habit which is very interesting in connection with the appa- 

 rently fixed habit of the Australian species. — W. G. 



A Key to the Royal Society Catalogue. 



"A Cataloguer" appears to have misunderstood me in 

 two points. In the index that I propose, the heads would not 

 be numbered. Again, in forming an estimate of the size of the 

 work, I made the supposition that the 8 papers of an author 

 could be grouped, not under 8, but under 3 heads. 



James C. McConnel. 



A Meteor. 



Last night (Monday, the 3rd), as I was crossing the Old 

 Deer Park to Richmond, I witnessed the flight of an exception- 

 ally fine meteor, which shone out with great brilliancy notwith- 

 standing the presence of a bright moon, which was almost at 

 the full. 



It appeared to start from the constellation of Leo, and travelled 

 across the sky to the westward, vanishing some 10° or 15° above 

 the horizon. 



The night was very quiet at the time, and I heard no report. 



T. W. Baker. 



Kew Observatory, Richmond, Surrey, March 4. 



THE DISCOVERY OF COAL NEAR DOVER. 



THE question of the existence of coal under the newer 

 rocks of Southern England, which has engaged the 

 attention of some of our leading geologists since the year 

 1 85 s, has found its final answer in the discovery announced 

 last week in the daily press. The story of the discovery 

 is a striking example of the progress of a scientific idea, 

 passing through various phases, and growing more clearly 

 defined through opposition and failure, until ultimately it 

 has been proved to be true, and likely to lead to industrial 

 changes of national importance. 



The question was originally started 35 years ago by 

 Mr. Godwin-Austen in a memorable paper brought before 

 the Geological Society of London, in which it was argued, 

 from the character and arrangement of the coal-fields and 

 associated rocks of Somersetshire and South Wales on 

 the west, and of the Belgian and North French coal-fields 

 on the east, that similar coal-fields lie buried beneath the 

 newer strata of the intervening regions. Mr. Godwin- 

 Austen pointed out that the general direction of the 

 exposed coal-fields was ruled by a series of great east 

 and west folds, running parallel to the great line of dis- 

 turbance — " the axisof Artois," — from the south of Ireland, 

 through South Wales and Northern Somerset on the 

 west, eastwards through Belgium and Northern France, 

 into the valley of the Rhine, near Diisseldorf. Through- 

 out this area the exposed coal-fields lie in long east and 

 west troughs. This series of folded Carboniferous and older 

 rocks formed also an east and west ridge along the line 

 of the axis of Artois, which gradually sank beneath the 

 waves of the Triassic, Liassic, Oolitic, and Cretaceous 

 seas. Against this the strata of the three first of these 

 rocks gradually thin off, while the coal-measures and 

 other rocks of the ridge have repeatedly been struck in 

 France and Belgium, and are now being worked imme- 

 diately underneath the Cretaceous strata over a wide 

 area. 



The axis of Artois also, where it is concealed by the 

 newer rocks in the south of England, is marked from 

 Somerset eastwards by the anticlinal of the chalk of 

 North Wiltshire, and the line of the North Downs, the 

 general law seeming to be " that when any great folding 

 and dislocation of the earth's crust has taken place, each 

 subsequent disturbance follows the very same lines, and 

 that simply because they are lines of least resistance." 



Mr. Godwin-Austen, by combining all these observa- 

 tions, finally concluded that there were coal-fields beneath 

 the Oolitic and Cretaceous rocks of the south of England, 



