May i, 1913] 



NATURE 



219 



explains these facts on the supposition that the , 

 cause is not to be sought in the mechanism of 

 the ear alone, but in the relation of this mechanism 

 to different parts of the brain. 



The paths by which nervous impulses, gener- 

 ated by a sonorous vibration, say, in the cochlea, 

 are communicated to the brain, are very com- 

 plicated, and come into anatomical connection 

 with many nervous centres. Such centres may be 

 considered as being of higher and lower orders, 

 and the nervous impulses may pass from lower 

 to higher, calling forth at each stage a particular 

 sensation — say, that of a noise or of musical sensa- 

 tions—until they reach the highest cerebral centres 

 where there is the appreciation of all kinds of 

 auditory sensations, such as noises, music, and 

 speech. 



Prof. Marage's method of stimulating the ear 

 by his ingenious syren is well known. This in- 

 strument can transmit to the drumhead sonorous 

 waves of a measured intensity (that is, the air- 

 pressure is measured), and the special quality of 

 each vowel tone is produced by sending the waves 

 of pressure through resonators moulded on the 

 form of the mouth and throat cavities for each 

 vowel. Thus, by using the syren methodically, 

 the ear may be stimulated by tones that, as re- 

 gards both intensity and quality, are natural to 

 it, instead of tones produced by tuning-forks, or 

 noises, or by spoken words. Thus the ear and 

 the nerve centres may be put through a course 

 of education, a kind of drill, in short, produced 

 by the syren. The results are said to be very 

 encouraging with cases of whole or partial deaf- 

 mutism. 



Prof. Marage also gives in this pamphlet 

 copies of tracings of vowel-forms produced by 

 this syren which are well worthy of study, but 

 he does not mention how these beautiful photo- 

 graphs were obtained. The gist of the whole 

 matter is that in attempting to explain auditory 

 mechanisms, we must not confine our attention to 

 the ear alone, but to the ear as associated with 

 auditory nerve centres. The investigation, in 

 short, becomes more and more complicated. 



John G. McKendrick. 



NATURAL HISTORY IN CEYLON. 

 CPOLIA ZEYLANICA is an excellent quarterly 

 ^ publication designed to promote a knowledge 

 of the natural history of Ceylon and its surround- 

 ing seas. It was established by Prof. A. Willey 

 (now at Montreal) some eight or nine years ago 

 when he was director of the Colombo Museum, 

 and has been kept up since with admirable skill 

 and energy by his successor, Dr. Joseph Pearson, 

 the present editor. The part for January, 1913, 

 contains, along with several notes on land and 

 fresh-water animals, three articles of special 

 interest on pearl-oyster fisheries. 



The first article, by Captain Legge, "Master 



Attendant " at Colombo and inspector of the 



pearl banks, is semi-popular, and is written 



rather from the navigator's and the historian's 



NO. 2270, VOL. 91] 



point of view, containing notes and stories of 

 fisheries and celebrated pearls. Here and there 

 in Captain Legge 's chatty account of his personal 

 adventures on the pearl banks one comes on quite 

 important observations, such as, when describing 

 a walk in diving-dress over the sea-bottom : 



Immediately I walked off the "paar" I was upon 

 very loose sand, in waves like giant furrows in a 

 ploughed field; whilst for quite two feet high above 

 the ground there was sand in suspension. Here 

 oysters are covered up, buried and destroyed imme- 

 diately. 



Yet some recent writers have argued that there 

 can be no movement of the sand on the bottom, 

 and that beds of oysters cannot be silted up by 

 moving sand. 



Captain Legge gives us an additional instance 

 of the now well-known danger to beds of oysters 

 from predatory elasmobranch fish, as follows : 



At the inspection in November, 1902, I decided that 

 a certain bed was quite the gem of those to be fished 

 in March, 1903; the oysters were larger and older 

 than any others I had inspected, and were very 

 plentiful ; however, as I was passing over this spot on 

 my way back at the end of the inspection, I observed 

 a very large shoal of rays in the vicinity. In the 

 following March, about the second week of the 

 fishery, I moved to this my pet bed of oysters, only, 

 however, to be told by the divers that there were no 

 living oysters there. I at once descended in the 

 diving dress and found the bottom of the sea strewn 

 with empty oyster shells, each valve turned nacre 

 upwards and shining, giving a very curious effect, 

 whilst each shell or valve was broken obviously by 

 external pressure into three pieces. This could only 

 have been done by the powerful jaws and teeth of 

 the ray. 



The second article is a well-considered, judicial 

 account of the scientific work on the Ceylon pearl 

 banks in the last decade, 1902 to 1912, by the 

 editor, Dr. Pearson, director of the Colombo 

 Museum and Government Marine Biologist. Dr. 

 Pearson passes in review the scientific explora- 

 tion of the pearl banks in 1902, the recommenda- 

 tions in Prof. Herdman's report to the Govern- 

 ment, the formation of a financial syndicate in 

 1906 to take over a twenty years' lease of the 

 fisheries at a large annual rental, their two highly 

 profitable fisheries which cleared the ground of 

 adult oysters, and then the subsequent failure of 

 yield and resulting barren condition of the banks. 

 The various operations suggested and performed 

 are discussed, and the conclusion is reached that : 

 The work subsequent to Herdman's reports gives 

 very little evidence that his recommendations have 

 been carried out seriously. 



Dr. Pearson brings together a good deal of 

 argument in favour of the possibility of oyster- 

 beds being buried and lost by movements of the 

 sand, and he quotes some personal observations, 

 made on the bottom by the inspector of pearl 

 banks, such as : 



What impressed me most was that the spots I 

 dived on last March, which were then level rock, with 

 a coating of 3 or 4 in. of sand, had now as much as 

 a foot of sand in places. All over the sand was in 

 fairlv deep ridges, not so deep as the ridges of the 



