Page images
PDF
EPUB
[graphic]
[ocr errors]

THE SHELL-COLOURING OF NON-MARINE MOLLUSCA.

BY WILFRED MARK WEBB, F.L.S.

HE theory brought
forward by Mr.
J. W. Williams*
with regard to the
primitive colouring
of non-marine shells
has already been
discussed at length
by Mr. S. Pace †
and Mr. C. Clare
Fryer, but the
latter writer has
brought forward
some very interest-
ing points, and Mr.
Williams's § reply
to the former critic
calls for further re-
marks.

Mr. Pace gives

an example of the want of clearness which he finds in Mr. Williams's writing; it can, however, be said, in favour of the latter, that authors even less lucid were quoted from, by the present writer in "The Universal Review." The meaning of the passage in question is, that "evolution of all kinds" has been from the simple to the complex. It is only necessary to bring forward the case of parasites in order to show the fallacy of such a statement, for, in many instances, although they had arrived at a stage of considerable differentiation before contracting their peculiar habits, they have since evolved in a downward direction. Mr. Williams gives it to be understood, in the concluding paragraph of his article, that he has studied Darwin's works, but in "The

[graphic]

"The Colouring and Banding in Land and Freshwater Shells," SCIENCE-GOSSIP, August, 1890, p. 178.

+"The Colouring and Banding of Freshwater Shells," SCIENCE-GOSSIP, October, 1890, p. 233.

"The Colouring and Banding in Land and Freshwater Shells," SCIENCE-GOSSIP, November, 1890, p. 241.

Ibid. SCIENCE-GOSSIP, December, 1890, p. 274. "The Zoology of the Magazines," "Universal Review," October, 1890, p. 290.

No. 318.-JUNE 1891.

Origin of Species "* considerable space is given to discussing evolution "from the complex to the simple," and the following words occur:-" for natural selection, or the survival of the fittest, does not necessarily include progressive development."

To turn now to the various paragraphs in which the facts supposed by Mr. Williams, to support his theory, are set forth:

(1.) With regard to the constitution of the primary shell :-either Mr. Pace has some authority, with which the writer is unacquainted, for saying that it consists of conchyclin, or he has taken for granted that the tissue which forms this substance in the second instance, did so in the first. Has anybody analysed the primary shell? By-the-bye, the passage quoted from Balfour's 'Embryology' in Mr. Williams's reply occurs on page 189 (not on page 229 as stated). But in quibbling over chitin and conchyclin Mr. Williams misses the crucial point of the criticism, to wit, that as the substance of the primary shell is "naturally horn-coloured" it can have no bearing, in the matter of colouring, on the calcareous pigmented secondary shell, to the animal part of which it alone can possibly be compared.

(2). Even, allowing for a moment, that no pigment occurs in the very young secondary shell, one would not expect to find significant bands developed before the animal is free-living or while it is so small that shell-markings would apparently make no difference to it.

(3.) In his first article on the subject under consideration, Mr. Williams evidently meant to say that the majority of fresh-water Pulmonates were "horn. coloured and bandless." With regard to his reply, it must be said that it is not the part of a sane man to require from a questioner the "proofs of his statement." It would appear, that all Mr. Pace meant by asking how " environmental conditions" could be "less in water than on land" was to point out that the application of the adjective "less" to such a

"The Origin of Species," by Charles Darwin, F.R.S., 6th edition, p. 98.

G

noun as "conditions" is not good English, and that the phrase as it stands means nothing. Mr. Williams no doubt intended to convey the principle contained in the following passage from Darwin :

""*

"All fresh-water basins taken together make a small area, compared with that of the sea or land. Consequently the competition between fresh-water productions will have been less severe than elsewhere, new forms will have been then more slowly produced and old forms more slowly exterminated." (4.) Mr. Fryer's argument that white cannot be an advance in colour, is very good, and there are instances in which colour must have preceded albinism. Mr. Poulton thus speaks of the case of the albino peacock :

66

The regions in which 'structural' colours usually appear are readily recognisable, the white being of a different quality, the 'eyes' on the train coming out like a white damask table-cloth.

"Doctor Gadow informs me that the same fact is true of white ducks and drakes, the wing coverts, which are blue in normally pigmented individuals, exhibiting a peculiar sheen or gloss differing from the rest of the plumage. Doctor Gadow states that the structural colours are absent because the existence of a pigment beneath is necessary in order to show them off; and he points out that the ancestors of birds with such structural colours cannot well have been white because the effect depends in part upon pigment."+

(5.) There are in the writer's collection specimens of Helix rufescens in which the nucleus is of a darker brown than the rest of the shell.

Most specimens which he possesses of Helix arbus torum, H. nemoralis, H. hortensis, H. aspersa and H. Pomatia have a nucleus agreeing in colour with the "ground-tint" of the shell, thus in yellow, buff or brown examples of Helix nemoralis the apical whorl is correspondingly yellow, buff or brown.

Specimens of Helix Pisana from Tenby, Jersey, Guernsey and South Portugal have nuclei of a very dark brown colour, approaching black.

Of Helix virgata, H. ericetorum, H. caperata and H. acuta the nucleus is brown, corresponding in colour with the bands. White specimens of H. Pisana, H. virgata and H. ericetorum are also in the writer's possession which have no bands developed, but which nevertheless, retain the dark brown nucleus.

(6.) This paragraph depends on No. 4. The case of albino individuals of banded Helices is analogous to that of the white peacock which shows the "eyes" on its train, for in normal specimens of these snails the colours of the bands are accompanied by structural peculiarities in the shell, and in albino

* "The Origin of Species," by Charles Darwin, F.R.S., 6th edition, p. 83.

+"The Colours of Animals," by E. B. Poulton, F.R.S.,

note on p. 329.

forms the areas normally pigmented are marked by transparent zones. Therefore the whiteness is not a primary but a secondary feature.

(7.) Although Mr. Williams seems to have the best of the argument with regard to the immediate derivation of Cyclostoma elegans, it must be pointed out that the occurrence of this shell in Pleistocene fresh-water deposits is no argument in favour of his view, for truly, terrestrial forms abound in such deposits, that its colours no more support the theory than do those of the Helices. The Succinea can hardly be called fresh-water species!

(8.) What Mr. Fryer says with regard to the colours of the Hyalinia and Helices can in every way be endorsed by the present writer, who has given his attention to the subject for some years, and hopes to soon publish his conclusions with the evidence on which they are founded.

(9.) It is very probable that bands represent coalesced spots, the stripes of mammals in several cases undoubtedly originate in this way, but some of the species which Mr. Williams mentions, such as H. aspersa and H. virgata (other snails, Helix Pisana, H. acuta and H. vermiculata may be added) which have bandssome times represented by dots,† have only gained this style of marking secondarily, after the bands had already been evolved, for the apparent breaking up of the bands on these shells is due to the presence of striæ which really only obscure the band underlying them. The writer has tested this by cutting sections of the shell of Helix aspersa, also by scraping off the prominences from the same species and from H. vermiculata, and has since found that, Mr. Charles Ashford calls attention to this point. Mr. Ashford is perhaps one of "the few who have published their thoughts on this matter," but whose names are not given by Mr. Williams.

(10.) On taking into consideration the passage from Darwin quoted in No. 3, Mr. Williams's meaning will become clearer.

(11.) Mr. Fryer's references go to show that field-naturalists are not all of Mr. Williams's opinion with regard to the enemies of the genus Hyalinia. Paul Fischer, it may be noted, puts this genus with the Limacidæ not with the Helicidæ as does Mr. Pace.

[blocks in formation]

developed must be taken into consideration. The three assertions are (a) that the shell was originally "horn-coloured;" (8) that, secondly, it was white; (7) that bands arose as spots. The last head has been sufficiently discussed.

(a) If it be assumed that the shell was at first represented only by animal substance such as is produced in the shell-gland, it would certainly be horn-coloured-but this is arguing in a circle.

(B) If this primitive shell became calcareous it is likely that its appearance, owing to its containing little carbonate of lime, would be whitish or semitransparent-but it would not be homologous with the secondary shell, or assuming that the secondary shell arose in this way, the white flecks which occur in the shells of Limnea are at any rate more likely | to be a reversion to the more completely calcified shell of their marine ancestors, than a survival of a primitive whiteness, the tenuity of the shells of the Basommatophora having been acquired apparently in their present environment.

BOTANICAL NOTES FROM KEMSING AND ITS NEIGHBOURHOOD.

BEING

OEING anxious to call the attention of those interested in the local flora of England, I have collected a few notes this last summer on the flowering plants around Kemsing, and its neighbourhood, which may prove useful to some botanist. Kemsing, a tiny rural village, nestles on the slope of a long range of chalk hills, which stretch for many miles above the villages of Otford, Kemsing, Wrotham, and others, through that part of Kent known as "the Garden of Kent." It is the district along these hills of which I particularly wish to speak. Without exception, it is the most prolific spot for wild plants with which I have ever met.

The common plants-lovers of chalky soil-such as wild marjoram, field scabious (Knautia arvensis), Euphrasia officinalis, Scabiosa columbaria, Erythraa centaurium, Chlora perfoliata, Thymus serpyllum, Reseda lutea, Helianthemum vulgare (rock rose), which emblazons the mossy banks, with its associate, Polygala vulgaris, etc., grow most profusely up the grassy slopes, while in the woods higher up the hillside the sight of the great masses of Dipsacus sylvestris, in full bloom, and, mixed with that in the tangled underwood, thick beds of Senecio Jacobaa, is one really worth while going far to see.

Hypericum perforatum, Clematis vitalba, Ranunculus repens, Reseda luteola, Melilotus officinalis, Geranium Robertianum, Galeopsis tetrahit, and vast numbers of other common species in the Ranunculaceæ, Caryophyllacea, Umbelliferæ, Compositæ, Labiata, and Leguminosæ orders are found everywhere about there, in the lanes and on the hillsides.

Of the orchids I found but few, owing to the lateness of the season, but from various sources I learned

that it is a rich locality for them. All I came across were Ophrys apifera, Orchis pyramidalis, Gymnadenia conopsea, and in the woods just above Kemsing, some splendid spikes of Epipactis latifolia, in full bloom. Ophrys muscifera abounds in June, besides most of the commoner species; Orchis hircina (lizard orchis), is to be met with, but is very rare.

Thanks to the kind directions of a local botanist, of Ightham, I was lucky to find some fine plants of Atropa belladonna in an old chalk-pit near Wrotham. The plant grows nearer Kemsing, but I failed to find the spot. The lane (Pilgrim's Road), below Beechy Lees, near Kemsing, affords fine specimens of Trifolium fragiferum, Lepidium campestre, and Linaria vulgaris, and farther down a lane, which crosses the railway line between Kemsing and Seal, I discovered a corner where dwelt some Thlaspi arvense (honesty), and Lathyrus macrorrhizus.

At Beechy Lees, in the lane there, are two goodsized plants of Lithospermum officinale; this plant grows but sparingly. A slight declivity in the hillside near Kemsing is ablaze with masses of Papaver somniferum-I never saw a more luxuriant growth of them. Amongst the other lovers of the downs are Gentiana amarella, Fragaria vesca, and in the cornfields on the range, Anagallis arvensis, Valerianella dentata, Linaria spuria, Anthirrinum orontium, and a small quantity of Anagallis arvensis, var. cærulea. Farther along we find Nepeta cataria (cat-mint), Mentha arvensis, Spergula arvensis, Echium vulgare, Filago germanica, and others. I saw a specimen of Lathyrus aphaca, just gathered on the hills, but found none myself. Space forbids of my mentioning other plants more particularly, but I would strongly urge any one, who cares for botanising, to run down and pay a visit to the Kentish hills and lanes around Kemsing on the earliest opportunity.

K. E. STYAN.

OUR LANE.

[Continued from p. 101.]

L

IMITED space precludes me from dwelling at length upon the curious forms of insect and molluscan life that are to be found in our lane. I cannot, however, refrain from describing a creature probably unfamiliar to many naturalists. One gloriously bright day, during the past summer, I was reclining upon the close-cropped turf on the summit of the Down, when, hard by, my eye happed upon a tiny holeabout large enough to admit a small pea. Presently, some half inch adown it, I see an object slowly rising-it stops-and for some few minutes I keep my eye riveted upon it. Slowly, very slowly, again it upward moves-reaches the margin of the hole, then once again stops. So nicely adjusted in size to the orifice is the object, and so exactly does it assimilate to the earth in color, that, it is hard to

[ocr errors]

believe that any hole exists. Still patiently I watch until a tiny, red velvety-jacketed spider, unsuspecting of danger, runs in a line directly across the treacherous path. In less than the twink of an eye a sharp click-spider and trap-door together disappear -and lo! in place thereof a hole is once more open to my inquisitive eye. 'Tis the burrow of the larva of that most beautiful of all English insects the tiger beetle (Cicindela campestris), and that nicely fitting trap-door was its flattened head, armed with a terrible pair of jaws, on which, if once impaled, no victim will ever find escape.

The larva of the tiger beetle is a remarkable instance of the adaptation of an animal to the conditions of its existence. 'Tis a curiously unattractive specimen of insectivity when exhumed, and it will at once be seen that it has been furnished with special organs fitted for the performance of special work. These consist of a pair of tubercles, situated on the upper side of the soft abdomen, to these are attached two hooks, each surrounded by a series of stiff bristles. These curious appendages enable the creature to climb up, and retain its position

Fig. 87.-Helix hispida.

Fig. 86.-Helix aspersa.

in any part of its smooth burrow, which, without some such arrangement, it would be impossible for it to do. Its flattened head, which is furnished with six eyes, not simply serves the purpose of an efficient shield, but is, also, a powerful implement, which enables its possessor to cast out with facility the excavated earth. Small pellets of sand, or loam, and particles of rock introduced into the burrow are ejected with wonderful precision and considerable force, as are, also, the exuvia of its victims. A sharp unmistakable click is heard, and the particle is shot forth as a bomb from a mortar. When visible, gently touch the shield-like head with a slender blade of grass, the click which accompanies the lightning-like backward movement of the head indicates that the object has unerringly been struck, and the slight start of the operator almost invariably jerks the uncanny looking creature from its burrow. When the larva is about to change into the pupal condition, it securely barricades its burrow with a diaphragm of earth, and in due time emerges a beetle, resplendent in a panoply of emerald and ruby, garnished with burnished gold, but endowed with instincts little in accord with its beauteous aspect.

The burrows are numerous in the sun-scorched banks and indurated footpaths at the top of our lane. Space will not allow of my describing many other curious forms of insect life, but winged creatures both dipterous and hymenopterous, and of "forms and hues divine," abound. Well represented are the butterflies and moths : amongst the former the least common are the beautiful brimstone (Gonepteryx Rhamni) and the dark-green fritillary (Argynnis Aglaia), but some of the most richly coloured kinds are abundant, the painted lady (Cynthia Cardui) and the peacock (Vanessa Io) particularly so; the red admiral (Vanessa Atalanta), I seldom light upon, whilst the commonest form in my orchard and neighbourhood is the small tortoiseshell (V. Urtica). Of course the pretty orange-tip (Anthocaris Cardamines) is, at times, plentiful; nor must I forget that charming though by no means rare blue-the chalkhill blue (Polyommatus Corydon). The speckled wood (Lasiommata Ægeria), the wall (L. Megara), and the green hair-streak (Thecla Rubi), besides a host of commoner species, sport in the summer sunshine, and proclaim the richness of the locality in these "things of beauty."

Of all the many species of moths to be met with I have found the burnet to be wonderfully plentiful at

[graphic]

SWQ

Fig. 88.-Helix arbustorum.

the lane-top, and the exquisite little twenty-plume (Alucita hexadactyla) equally abundant in my garden. All through the year-except during the coldest months-three or four to a dozen, and upwards, may always be found under the shelter of my stone, honeysuckle covered porch, very many specimens hybernating in our bedroom and dark closets.

As might be expected, the Ichneumonidæ are in full force; their name is Legion, and many and curious are their nests to be found in the neighbourhood of our lane. The mud-wasps, too, build their mud-cells in nearly every sunny crevice in the woodwork of our summer-house, in which are stored the living caterpillars which serve as food for the young grubs when hatched. Then, too, the solitary wasp (Vespa Norvegica) last summer hung its pretty pensile nest in a sheltered spot, o'erhung with ivy, and within but six inches of a spotted flycatcher's nest. Although in such close proximity, both creatures must have been peaceably engaged in their building operations at the same time. Several species of spiders that I have never before met with are to be found in the hedges, some I believe to be

rare.

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed]
« EelmineJätka »