54 



NATURE 



[May 16, 1889 



such I found to be actually the case on the slopes of Keeling 

 Atoll, where Captain Fitzroy's soundings were taken. Few, in 

 fact, who have read the work of the young naturalist of the 

 Beagle, can sufficiently realize how scanty were the data on which 

 the fundamental inference of the theory of subsidence was based ; 

 and I may safely add that few must be the scientific questions 

 that have been settled on a scantier basis of observation than 

 that relating to the depths at which reef-corals grow. 



With regard to the sections exhibiting the submarine profile 

 of the reef of Masamarhu Island, I was first at a loss to under- 

 stand why their character should be advanced as favouring 

 the idea of a movement of subsidence, since, when they 

 first appeared in Nature (vol. xxxvi. p. 413), I regarded 

 them as favouring Mr. Murray's views. However, it soon 

 appeared that this opinion was based on our inextensive 

 acquaintance with the habits of corals, especially with the limit- 

 ing causes of their extension in depth. The "ditches" shown 

 in these sections I look upon as indicating the formation of 

 barrier-reefs at considerable depths, and as giving remarkable 

 support to my views on the origin of these reefs. In the paper 

 above quoted I have been led by the observations of Agassiz in 

 the Florida seas, and by my own in the Solomon Islands, to the 

 conclusion that the main determining condition of the depth in 

 which reef-corals thrive is to be found in the injurious effect on 

 coral growth of the sand and sediment produced by the breakers, 

 and that the distribution of these materials is dependent on 

 the angle of the seaward submarine slope and on other less 

 important circumstances. 



It follows from this that in those localities where the sub- 

 marine slope is moderate, a barrier-reef will f )rm beyond the 

 belt of detritus derived from the shore-reef inside it. But when 

 the slope is fairly steep, as in the case of Keeling Atoll, the 

 reef debris will cover an area of much less horizontal extent, 

 and, as at these islands, an off-lying line of coral shoals will 

 spring up at a distance only of 150 or 200 yards from the inner 

 reef. Should, however, the slope be precipitous, as at Masa- 

 marhu Island, the reef debris will extend to considerable 

 depths ; and beyond the area thus covered with sand and gravel, 

 a line of reef will in the course of time grow upwards, giving 

 rise to the so-called "ditches " of the sections. 



Reefs of all classes, as I hold, have a two-fold mode of 

 growth seawards. There is first the advancement of the outer 

 edge of a reef on its own talus, as dwelt upon by Mr. Murray. 

 In the second place, they grow seaward by a reclaiming pro- 

 cess, whether they be fringing, barrier, or circular reefs. The 

 distribution of the sand and debris, guided by the angle of the 

 submarine slope, determines, as above shown, this second mode 

 of growth, which may result, as at Keeling Atoll, in a line of 

 adjacent coral banks that ultimately reclaim a new strip and add 

 it to the width of the reef, or a more distant barrier reef may 

 appear at the surface, the lagoon of which silts up and is choked 

 with coral in the course of ages, or, as at Masamarhu Island, 

 there may occur a deeply-submerged barrier-reef that can be 

 discovered only by methodical soundings. 



Let us take the instance of Keeling Atoll to illustrate the 

 present condition of this controversy. In a series of papers on 

 this celebrated atoll, that I am preparing for the Royal Scottish 

 Geographical Society, I have shown that the direct evidence of 

 subsidence adduced in its case by Mr. Darwin is, according to 

 Mr. G. C. Ross, its present proprietor, founded in error. In 

 - truth, Mr. H, O. Forbes, during his visit in 1878, observed 

 evidence leading in his opinion towards a movement of upheaval. 

 In default, then, of direct evidence, we have to look for the 

 indirect proofs to certain a priori considerations, based on a 

 few soundings that appeared to demonstrate once and for all the 

 limit of depth of the reef-coral zone, a subject concerning which we 

 still have very incomplete data. Then we are transported across 

 the Indian Ocean to the go-fathom reef of Socotra, the origin of 

 which, for the reason ju:t stated, is hidden in mystery. After- 



■ wards, appeal is made to the thickness of reef limestones in 

 Cuba and in the Sandwich Islands, limestones which, it is 

 alleged, could only have been formed during subsidence, not- 



■ withstanding that their exact nature has not yet been deter- 

 mined, and in spite of the circumstance th?t reefs can attain a 

 consideral)le thickness, as Mr. Murray rightly holds, solely by 

 their outward growth. 



If a visitor from another planet, having thus fa- followed the 



discussion, were to inquire in an apologetic manner whether, 



instead of going to the other hemisphere for evidence wa had 



'methodically endeavoured to investigate the problem on the 



spot, by patiently studying the complex agencies at work on 

 this atoll, by carefully inquiring into the changes of the past, 

 and by interpreting through their aid the proce-ses of the 

 present, we should be obliged to answer: " .Scarcely at all. A 

 theory advanced on the very threshold of such an investigation 

 explained so well our limited knowledge by a movement of 

 subsidence, that it is only of late years that doubts have arisen 

 and that a new theory has been advanced opening up the lines 

 of research to which you refer." H. B. Guppy. 



" Bambangala." 



I SHALL be glad if you will allow me to call the attention of 

 those who visit the Congo Free State to the curious antelope 

 called " Bambangala," which is spoken of by Captain Bateman 

 in his "The First Ascent of the Kasai," lately published by 

 Messrs. George Philip and Son. Captain Bateman describes it 

 as being " in size as large as a mule ; of a bright chestnut colour, 

 striped with creamy white, much in the manner of a zebra, on 

 the back and sides, and dappled on the neck and flanks." 



From the form of the horns shown in the figure (which, by 

 the kind permission of Messrs. George Philip and Son, is here 

 reproduced from Captain Bateman's book), it would appear that 

 this antelope must belong to the genus Tragelaplms, but probably 

 to a new species. 



I should be very glad to examine specimens of the head and 

 horns of this antelope, in case any of your correspondents in the 

 Congo should meet with it, or to have some further information 

 on the subject from those who have visited that region. 



P. L. SCLATER. 



Zoological Society of London, 3 Hanover Square, 

 London, W. , May 7. 



Inclusion of the Foot in the Abdominal Cavity of a 

 Duckling. 



A DUCKLING, four days old, sent from Eastry in Kent, hatched 

 on April 25, 1889, presented the above curious abnormality. 

 The ngiit lower extremity was normal in every respect ; the left 

 appeared on superficial examination to be absent. An incision 

 made through the skin over the left flank at once disclosed the 

 left limb, the joints being flexed to their utmost extent, and 

 the thigh adducted, so that it lay in contact with the ab- 

 dominal muscles of the left side ; at the tibio-tarsal joint the 

 limb passed through the wall of the abdomen, a few millimetres 

 above the symphysis pubis. A portion of the yolk-sac protruded 

 at the aperture by which the foot penetrated tlie abdominal 

 wall. Opening the abdomen showed the rennind.-rof the yolk- 

 sac, its connection with the ileum, and the left foot lying upon 

 the surface of the intestines. This included foot was fully 

 developed, having a complete web, an 1 being covered with 

 scales. An adhesion exi.sted between the outer surface of the 

 yolk-sac and the left leg in the region of its tibio-tarsal joint, and 

 there were also adhesions of the sac to the skin of the abdomen, 



