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Art. XVII.—The Bipolar Theory.
[Read before the Wellington Philosophical Society, 2nd October, 1907.]
Since my paper on the evidence for the bipolar theory in the littoral marine fauna of New Zealand* was written I have gathered a few more scraps, which may be taken as supplementary.
Mr. F. Chapman, Palæontologist to the National Museum, Melbourne, who described the Foraminifera recently dredged up from 110 fathoms off the Great Barrier Island, says, “Another interesting feature of the present assemblage of Foraminifera is the presence of a large number of forms which have hitherto been found in dredgings from other, widely removed, areas, generally in the Northern Hemisphere; and particularly from the colder waters of the Temperate Zone.“†
Three species of marine Bryozoa besides those given in my former paper appear to be common to New Zealand and the North Atlantic—namely, Cellaria fistulosa, Europe and New Zealand; Plumatella princeps, identical with or closely allied
[Footnote] * Trans. N.Z. Inst., vol. xxxix, p. 131.
[Footnote] † Trans. N.Z. Inst., vol. xxxviii, p. 77.
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to the European form; and ætea recta, Arctic and Europe, closely related to æ. anguina.
The nudibranch mollusc Goniodoris castanea occurs in New Zealand and Britain. The genus Homoiodoris has only two known species—one (H. neozelanicus) occurs in New Zealand, and the other in Japan.
The enteropneust Dolichoglossus otagoensis, Benham, has a grooved proboscis, “which is only known in one other species (D. sulcatus, Spengel) from Japan; and the polynoid Physalidonotus squamosus (Lepidonotus giganteus, Kirk) represents peculiarities, indicated by its generic name, that have hitherto only been noted in two Japanese polynoids, recently described by Moore as Lepidonotus branchiferus and L. chitoniformis, but which probably should be included in Ehler's new genus just mentioned.” (Benham.)
A sea-star from Japan closely allied to our common littoral form Asterias calamaria has been described by Doederlein under the name A. calamaria, var. japonica.* The New Zealand species occurs also on the east coast of Australia and in Mauritius.
Although there is but little evidence for bipolarity in our land fauna, the fresh-water fauna contains many bipolar forms. Retropinna richardsoni is the southern representative of the smelt of northern Europe and America.
Of the 130 species of Infusoria given in the “Index Faunæ,” no less than eighty-four are said to be identical with European forms. I cannot say that these identifications are correct, but Maskell, who was a good observer, and had a great deal of experience in the determination of microscopic forms (Desmideœ, Coccidœ, and Aleurodidœ), told me shortly before his death that, on account of doubts expressed by a European naturalist, he had reviewed his identifications, and had concluded that our species could not be separated from those of Europe.
Of the forty-two species of Rotifera recorded from New Zealand, thirty-four are European.
The fresh-water sponge Spongilla lacustris occurs in our streams and lakes, and also the common European hydra (H. viridis), and a species of Cordylophora, which, if not identical, is nearly related to C. lacustris.
“The fresh-water shell Latia, which is living in New Zealand, is fossil in North America. It is closely related to Gundlachia, which inhabits Tasmania and North America…. The fresh-water spider Cambridgea is almost identical with Argyroneta of Europe.” (Hutton.)
[Footnote] * Zool. Anz., xxv, p. 332.
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A number of New Zealand plants, especially those of the mountains, have representative forms in Europe and America. The tutu (Coriaria) may be taken as an example. “Our common tutu (Coriaria ruscifolia) occurs equally commonly on the Chilian Andes; the smaller-leaved mountain form (C. thymifolia) ranges along the whole chain of the Andes from Chili up to Mexico; while the little narrow-leaved form (C. angustissima) appears to be confined to the mountains of the southern part of the colony. Besides these, two or three other species occur in southern Europe, in the Himalayan region, and in Japan.” (Thomson.)
The facts regarding the distribution of our fauna and flora which have been recorded appear to prove the close alliance of a large number of species with those of the northern temperate and sub-Arctic regions; and, if some of the forms now supposed to be identical are ultimately found to be distinct, their near relationship is, however, undoubtedly established.
The most probable explanation of the occurrence of the same or closely allied species of plants and animals at widely separated stations is that they occupied continuous areas of distribution in remote times, when the physical conditions on the earth—climate and distribution of land and water—were different from what they are now.
Very few of our higher forms of animal-life have representatives in the north, but the number of representative and identical species increases as we go down to the lower forms. Mr. A. McKay informs me that the same obtains among the fossils. And, as regards time, a number of our Upper Tertiary fossils are nearly related to or identical with northern forms; the number increases in the Lower Tertiary, and goes on increasing through the Mesozoic formations, till we come to the Palæozoic forms, almost all of which appear to be identical or nearly related to those of northern Europe and America.
We much need a Palæontology of New Zealand; a great quantity of material has been collected, and is waiting in Welbngton to be worked up, but a New Zealand palæontologist has not yet come.