NATURE 



337 



rHlRSDAV. AUGUST n, 1904. 



SXHR.W. HISTORY OF THE M.M.DIVES 



.4 -YD LACCADIVES. 



llw Fauna and Geography of the Maldive and 



I.aceadive Archipelagoes. Edited by J. S. Gardiner. 



\ ol. i., parts ii. to iv. ; vol. ii., parts i. to iii. (Cam- 



bridfje : C. J. Clay and Sons, 1902-4.) 

 A .S the general scope and character of this important 

 -i »- work were referred to at some length in a notice 

 of thr first part which appeared in Nature for .April 3, 

 U)o2 (vol. Ixv. p. 514), it will suffice on the present 

 occasion to confine attention to some of the more 

 generally interesting of the numerous memoirs con- 

 tained in the parts now before us. By generally 

 Interesting, we mean reports which deal more 

 especially with questions connected with morphology, 

 development, the limitations of species, reef-formation, 

 &-C.. rather than those devoted to systematic zoology, 

 and it is on these grounds that we pass over papers 

 like those by Messrs. Borradaile and Lanchester on 

 crustaceans, and the one by Mr. E. Smith on molluscs 

 (important as they are from their special point of 

 \ii\v) in favour of some of those of the former type. 



Especial interest concentrates, of course, on the 

 chapters (vol. i., parts ii. and iv.) devoted bv the editor 

 to the origin and mode of formation of the two archi- 

 pelagoes under survey. In the chapters included in 

 part ii., Mr. Gardiner, when stating his general views 

 nil this part of the subject, definitely and unhesitatingly 

 rejects the theory that the two archipelagoes can have 

 been formed by the subsidence of a large central 

 island, the topography of the central deep plateau 

 being, in his opinion, unfavourable to such a view. 

 On the contrary, he maintains the former existence 

 ol continuous land over the area, which was planed 

 down by the action of currents to an almost flat plateau 

 ;it a depth of about 160 fathoms, and that on this 

 (jlalcau the different banks originated independently 

 b\ the slow growth of deep-sea corals, assisted in some 

 small degree by nullipores, &c., but completed by the 

 subsequent growth of a superficial reef formed by true 

 corals and nullipores, aided by a general outward 

 extension of the growing reef by current-borne detritus. 

 When the superficial reef approached the surface, it is 

 considered probable that some land was formed by 

 elevation, or by a change in the level of the ocean. 

 Finally, in the individual atolls the lagoon was formed 

 partially by the more rapid growth of the organisms 

 on the edge of the bank, thereby building up an 

 encircling reef, and partially by the subsequent erosion 

 of the central area. The author adduces evidence to 

 show that certain kinds of coral will grow freely 

 at depths of considerably more than 200 fathoms, 

 and he adds that his views with regard to reef 

 and atoll formation hold good for the islands 

 ol the Pacific as well as for those of the Lacc.idive and 

 Maldive Archipelagoes. In the chapter in part iv. 

 details are given of the various atolls, with remarks 

 on apparent recent changes in the archipelagoes and 

 on the death of corals. 



XO. 1815, \t [ . 70] 



Passing on to the purely zoological reports, we may 

 notice that in dealing with the Chsetognatha (Sagitta 

 and its allies), Mr. Doncaster comments gn the un- 

 stable character of the species in this group, several 

 of which seem to graduate into others. Most re- 

 markable is the fact that such species do not appear 

 to be separated either geographically or in habit, closely 

 allied forms living in the same locality under similar 

 conditions. Consequently, it is difficult to believe that 

 they can have been differentiated by natural selection. 

 In his notice of the echiiioderms, Prof. F. J. Bell 

 corroborates previous observations as to the loss of 

 the upper surface of the disc in many feather-stars 

 (ophiurids), and further points out that if gonads are 

 set free by the loss of this disc, and a new disc and 

 new -onads are subsequently formed, the question of 

 germ-plasm may be regarded as answered. 



.\nother group which has yielded results of special 

 interest is that of the alcyonarian polyps, the collec- 

 tion made by Mr. Gardiner's expedition serving to 

 show, according to Prof. Hickson, the untrustworthy 

 character of species formed on the evidence of single 

 specimens. The large series of examples now for the 

 first time available demonstrates the variation in form, 

 colour, and other features of what appears to be one 

 and the same specific type when collected over a large 

 area. If, for instance, a specimen of organ-pipe coral 

 (Tubipora) were collected in Celebes and a second in 

 the Maldives, there is little doubt that they would be 

 regarded as representing two distinct species, but a 

 walk at low tide along a Maldive reef would reveal 

 the existence of a number of intermediate types con- 

 necting the two supposed species by imperceptible 

 gradations. These organisms, in fact, exhibit a 

 number of " facies," which have not local limitations. 



" If each facies," observes Prof. Hickson, " repre- 

 sents a species, then we have the remarkable pheno- 

 menon of a number of closely related species distributed 

 over a wide area and competing in the struggle for 

 existence, with approximately equal success, in many 

 localities of this area. If, on the other hand, all the 

 facies represent but one species, then we have a species 

 capable of extraordinary variation in circumstances 

 apparently identical." 



Without recourse to cross-breeding, it is impossible 

 to demonstrate which of the two propositions is true, 

 and the only practical course is therefore to regard as 

 species all the unconnected types. 



The species question is resumed in the chapters on 

 madreporiform corals (vol. ii. part iii.), where Mr. 

 (iardiner remarks that he has found much less 

 difficulty in finding the limitations of species among 

 the AstreidK than was experienced by Mr. Bernard in 

 the case of the perforate group. The puzzle will, he 

 thinks, in both cases be solved by definitely ascertain- 

 ing which variations are discontinuous and which con- 

 tinuous. Here occasion is taken to notice the favour- 

 able conditions presented by corals for the study of vari- 

 ation, owing to the fact that the larvae have no choice 

 in their environment. Unless there be real action on 

 the part of the local environment in producing dis- 

 continuous variation in the gametes of new 

 immigrants, it will be obvious that the species must 

 rcniaiii .ipproximately constant. 



O 



