Two small bats of N. American species also occasionally reach the island, while two others from the West Indies have more rarely occurred, and these are the only wild mammalia except rats and mice.
_Insects of Bermuda._--Insects appear to be very scarce; but it is evident from the lists given by Mr. Jones, and more recently by Professor Heilprin, that only the more conspicuous species have been yet collected. These {270} comprise nineteen beetles, eleven bees and wasps, twenty-six b.u.t.terflies and moths, nine flies, and the same number of Hemiptera, Orthoptera, and Neuroptera respectively. All appear to be common North American or West Indian species; but until some competent entomological collector visits the islands it is impossible to say whether there are or are not any peculiar species.[57]
_Land Mollusca._--The land-sh.e.l.ls of the Bermudas are somewhat more interesting, as they appear to be the only group of animals except reptiles in which there are any peculiar species. The following list was kindly furnished me by Mr. Thomas Bland of New York, who has made a special study of the terrestrial molluscs of the West Indian Islands, from which those of the Bermudas have undoubtedly been derived. The nomenclature has been corrected in accordance with the list given in Professor Heilprin"s work on the islands. The species which are peculiar to the islands are indicated by italics.
LIST OF THE LAND-Sh.e.l.lS OF BERMUDA.
1. Succinea fulgens. (Lea.) Also in Cuba.
2. ,, Bermudensis. (Pfeiffer.) ,, Barbadoes (?)
3. ,, margarita. (Pfr.) ,, Haiti.
4. _Poecilozonites Bermudensis._ (Pfr.) A peculiar form, which, according to Mr. Binney, "cannot be placed in any recognised genus."
A larger sub-fossil variety also occurs, named _H. Nelsoni_, by Mr. Bland, and which appears sufficiently distinct to be cla.s.sed as another species.
5. ,, _circ.u.mfirmatas_ (Redfield.)
6. ,, _discrepans._ (Pfr.)
7. ,, _Reinia.n.u.s._ (Pfr.)
8. Patula (Thysanophora) hypolepta (Shuttleworth.)
9. ,, vortex. (Pfr.) Southern Florida and West Indies.
10. Helix microdonta. (Desh.) Bahama Islands, Florida, Texas.
11. ,, appressa. (Say.) Virginia and adjacent states; perhaps introduced into Bermuda.
{271} 12. ,, pulch.e.l.la. (Mull.) Europe; very close to _H.
minuta_ (Say) of the United States. Introduced into Bermuda (?)
13. ,, ventricosa. (Drap.) Azores, Canary Islands, and South Europe.
14. Bulimulus nitidulus. (Pfr.) Cuba, Haiti, &c.
15. Stenogyra octona. (Ch.) West Indies and South America.
16. Stenogyra decollata (Linn.) A South European species.
Introduced.
17. Coecilianella acicula. (Mull.) Florida, New Jersey, and Europe.
18. Pupa pellucida. (Pfr.) West Indies, and Yucatan.
19. ,, Barbadensis. (Pfr.) Barbadoes (?)
20. ,, Jamaicensis. (C. B. Ad.) Jamaica.
21. Helicina convexa. (Pfr.) Barbuda.[58]
Mr. Bland indicates only four species as certainly peculiar to Bermuda, and another sub-fossil species; while one or two of the remainder are indicated as doubtfully identical with those of other countries. We have thus about one-fifth of the land-sh.e.l.ls peculiar, while almost all the other productions of the islands are identical with those of the adjacent continent and islands. This corresponds, however, with what occurs generally in islands at some distance from continents. In the Azores only one land-bird is peculiar out of eighteen resident species; the beetles show about one-eighth of the probably non-introduced species as peculiar; the plants about one-twentieth; while the land-sh.e.l.ls have about half the species peculiar. This difference is well explained by the much greater difficulty of transmission over wide seas, in the case of land-sh.e.l.ls, than of any other terrestrial organisms. It thus happens that when a species has once been conveyed it may remain isolated for unknown ages, and has time to become modified by local conditions unchecked by the introduction of other individuals of the original type.
_Flora of Bermuda._--Unfortunately no good account of the plants of these islands has yet been published. Mr. {272} Jones, in his paper "On the Vegetation of the Bermudas" gives a list of no less than 480 species of flowering plants; but this number includes all the culinary plants, fruit-trees, and garden flowers, as well as all the ornamental trees and shrubs from various parts of the world which have been introduced, mixed up with the European and American weeds that have come with agricultural or garden seeds, and the really indigenous plants, in one undistinguished series. It appears too, that the late Governor, Major-General Lefroy, "has sown and distributed throughout the islands packets of seeds from Kew, representing no less than 600 species, princ.i.p.ally of trees and shrubs suited to sandy coast soils"--so that it will be more than ever difficult in future years to distinguish the indigenous from the introduced vegetation.
From the researches of Dr. Rein and Mr. Moseley there appear to be about 250 flowering plants in a wild state, and of these Mr. Moseley thinks less than half are indigenous. The majority are tropical and West Indian, while others are common to the Southern States of North America; the former cla.s.s having been largely brought by means of the Gulf Stream, the latter by the agency of birds or by winds. Mr. Jones tells us that the currents bring numberless objects animate and inanimate from the Carribean Sea, including the seeds of trees, shrubs, and other plants, which are continually cast ash.o.r.e and sometimes vegetate. The soap-berry tree (_Sapindus saponaria_) has been actually observed to originate in this way.
The only _species_ of flowering plant peculiar to Bermuda is _Carex Bermudiana_ (Hemsley), which is said to be allied to a species found only in St. Helena; but there are some local forms of continental species, among which are _Sisyrinchium Bermudianum_ and a variety of _Rhus toxicodendron_.
There are, however, two ferns--an Adiantum and a Nephrodium, which are unknown from any other locality. The juniper, which is so conspicuous a feature of the islands, is said to be a West Indian species (_Juniperus barbadensis_) found in Jamaica and the Bahamas, not the North American red {273} cedar; but there seems to be still some doubt about this common plant.
Mr. Moseley, who visited Bermuda in the _Challenger_, has well explained the probable origin of the vegetation. The large number of West Indian plants is no doubt due to the Gulf Stream and constant surface drift of warm water in this direction, while others have been brought by the annual cyclones which sweep over the intervening ocean. The great number of American migratory birds, including large flocks of the American golden plover, with ducks and other aquatic species, no doubt occasionally bring seeds, either in the mud attached to their feet or in their stomachs.[59]
As these causes are either constantly in action or recur annually, it is not surprising that almost all the species should be unchanged owing to the frequent intercrossing of freshly-arrived specimens. If a competent botanist were thoroughly to explore Bermuda, eliminate the species introduced by human agency, and investigate the source from whence the others were derived and the mode by which they had reached so remote an island, we should obtain important information as to the dispersal of plants, which might afford us a clue to the solution of many difficult problems in their geographical distribution.
_Concluding Remarks._--The two groups of islands we have now been considering furnish us with some most instructive facts as to the power of many groups of organisms to pa.s.s over from 700 to 900 miles of open sea.
There is no doubt whatever that all the indigenous species have thus reached these islands, and in many cases the process may be seen going on from year to year. We find that, as regards birds, migratory habits and the liability to be caught by violent storms are the conditions which determine the island-population. In both islands the land-birds are almost exclusively migrants; and in both, the non-migratory groups--wrens, t.i.ts, creepers, and nuthatches--are absent; while the number of annual visitors is greater in proportion as the migratory habits and prevalence of storms afford more efficient means for their introduction. {274}
We find also, that these great distances do not prevent the immigration of some insects of most of the orders, and especially of a considerable number and variety of beetles; while even land-sh.e.l.ls are fairly represented in both islands, the large proportion of peculiar species clearly indicating that, as we might expect, individuals of this group of organisms arrive only at long and irregular intervals.
Plants are represented by a considerable variety of orders and genera, most of which show some special adaptation for dispersal by wind or water, or through the medium of birds; and there is no reason to doubt that besides the species that have actually established themselves, many others must have reached the islands, but were either not suited to the climate and other physical conditions, or did not find the insects necessary to their fertilisation, and were therefore unable to maintain themselves.
If now we consider the extreme remoteness and isolation of these islands, their small area and comparatively recent origin, and that, notwithstanding all these disadvantages, they have acquired a very considerable and varied flora and fauna, we shall, I think, be convinced, that with a larger area and greater antiquity, mere separation from a continent by many hundred miles of sea would not prevent a country from acquiring a very luxuriant and varied flora, and a fauna also rich and peculiar as regards all cla.s.ses except terrestrial mammals, amphibia, and some groups of reptiles. This conclusion will be of great importance in those cases where the evidence as to the exact origin of the fauna and flora of an island is less clear and satisfactory than in the case of the Azores and Bermuda.
{275}
CHAPTER XIII
THE GALAPAGOS ISLANDS
Position and Physical Features--Absence of Indigenous Mammalia and Amphibia--Reptiles--Birds--Insects and Land-Sh.e.l.ls--The Keeling Islands as Ill.u.s.trating the Manner in which Oceanic Islands are Peopled--Flora of the Galapagos--Origin of the Flora of the Galapagos--Concluding Remarks.
The Galapagos differ in many important respects from the islands we have examined in our last chapter, and the differences are such as to have affected the whole character of their animal inhabitants. Like the Azores, they are volcanic, but they are much more extensive, the islands being both larger and more numerous; while volcanic action has been so recent that a large portion of their surface consists of barren lava-fields. They are considerably less distant from a continent than either the Azores or Bermuda, being about 600 miles from the west coast of South America and a little more than 700 from Veragua, with the small Cocos Islands intervening; and they are situated on the equator instead of being in the north temperate zone. They stand upon a deeply submerged bank, the 1,000 fathom line encircling all the more important islands at a few miles distance, whence there appears to be a comparatively steep descent all round to the average depth of that portion of the Pacific, between 2,000 and 3,000 fathoms. {276}
[Ill.u.s.tration: MAP OF THE GALAPAGOS AND ADJACENT COASTS OF SOUTH AMERICA.]
The light tint shows where the sea is less than 1,000 fathoms deep.
The figures show the depth in fathoms.
The whole group occupies a s.p.a.ce of about 300 by 200 miles. It consists of five large and twelve small islands; the largest (Albemarle Island) being about eighty miles long and of very irregular shape, while the four next in importance--Chatham, Indefatigable, James, and Narborough Islands, are each about twenty-five or thirty miles {277} long, and of a rounded or elongate form. The whole are entirely volcanic, and in the western islands there are numerous active volcanoes. Unlike the other groups of islands we have been considering, these are situated in a comparatively calm sea, where storms are of rare occurrence and even strong winds almost unknown. They are traversed by ocean currents which are strong and constant, flowing towards the north-west from the coast of Peru; {278} and these physical conditions have had a powerful influence on the animal and vegetable forms by which the islands are now inhabited. The Galapagos have also, during three centuries, been frequently visited by Europeans, and were long a favourite resort of buccaneers and traders, who found an ample supply of food in the large tortoises which abound there; and to these visits we may perhaps trace the introduction of some animals whose presence it is otherwise difficult to account for. The vegetation is generally scanty, but still amply sufficient for the support of a considerable amount of animal life, as shown by the cattle, horses, a.s.ses, goats, pigs, dogs, and cats, which now run wild in some of the islands.
[Ill.u.s.tration: MAP OF THE GALAPAGOS.]
The light tint shows a depth of less than 1,000 fathoms.
The figures show the depth in fathoms.