14 



NA TURE 



[May 4, 1876 



piano, evidently serve for excitation of different sensations 

 of tone. The organ of hearing of the Acridia is then, 

 simple, in a similar sense to that of the simple eyes which 

 perceive light, but not colours and forms ; and therefore it 

 closely approximates to the organs of touch, which like- 

 wise render sensible simple mechanical stimuli, and are 

 often arranged in a way similar to those organs of hearing. 

 The eye of the leech consists of a cup-like inflexion of 

 the skin, which is so lined with large transparent cells 

 that only a narrow axial canal remains. The nerve-stem 

 which enters at the bottom of the cup, fills this canal up 

 to a certain height, and ends there with a ganglion, while 

 the nerve-fibres pass into small cells, whose outer end 

 runs out into a short rod ; the entire cup is coated round 

 with a pigment skin and enveloped in muscles, which are 

 directed partly parallel, partly at right angles to the skin 

 surface, and therefore can draw the whole cup with its 

 sheath inwards, or press the contents somewhat outwards. 

 The former happens when the animal is surprised by 

 sudden light, just as we close our eyes in like circum- 

 stances. After some time, the leech opens its eyes, a part 

 of the glass-like cells on the rim of the open cup being 

 pressed out in form of a compact hemisphere. In this 

 way a pretty perfect visual apparatus is arranged. The 

 outer glass- like hemisphere corresponds to the light- 

 refracting medium of a more perfect eye. The mosaic 

 of rod-cells behind receives the separate rays and con- 

 veys the stimulus to the nerves, while the pigment layer 

 cuts off all round the light that has penetrated. Besides 

 these eyes on the upper lip, the leech possesses on other 

 parts of the body organs constructed quite similarly, only 

 without a pigment skin, so that they cannot be visual 

 organs. On the other hand, they are thrust out when the 

 animal is feeling about, and are thus evidently organs of 

 touch ; but at the same time the organs of sight are used 

 in the same way ; and when the animal sucks in the 

 liquids agreeable to it, it draws the upper lip with the open 

 organs of sight into the mouth. It would appear, then, 

 that these organs are at once the means of sensations of 

 touch, taste, and sight. To conceive this rightly we must 

 consider that in the lowest animals the special sensations 

 of sense are not yet differentiated ; their body is in all 

 parts alike sensitive, and sensation can only mean, quite 

 generally, ease or uneasiness. In a higher form of 

 organisation, certain body-parts are, by peculiar arrange- 

 ments, rendered sensitive to pressure, heat, light, and 

 chemical stimulation. But before such a simple organ 

 of sense develops in one direction for a particular 

 kind of stimulus, it can also communicate simple sen- 

 sations of a different kind. We ourselves know such a 

 combination of different sensations through the same organ 

 of sense ; g.^. our ear, at the boundary of the tone- 

 conductors, may feel, instead of tones, simply a vibra- 

 tion or a tickling, and thus has a sensation of touch 

 like that produced in a finger-point when a vibrat- 

 ing tuning-fork is applied to it. Again, in our tongue, 

 sensations of taste, smell, and touch are mixed together. 

 Thus the organ of hearing of Acridia, which can only 

 feel hissing noises, but no tones, may be compared, in 

 the quality of its sensation, to an organ of touch ; and 

 of the visual organ of the leech, it may perhaps be said 

 that it receives somewhat of the sensation of touch and 

 taste. In short, Ranke holds these organs to be of such 

 a kind that the general feeling is not yet fully separated- 

 into the categories of touch, hearing, seeing, &c. 



The ear of the Pterotrachea had long been known as a 

 bladder, on whose inner wall are tufts of hair, the motions 

 of which throw to and fro the otoliths or small spherical 

 stones freely suspended within the bladder. It was 

 believed that these continuous motions were connected 

 with the sensation of hearing. Ranke proves, however, 

 that they are merely due to convulsive movements of the 

 animal in dying under the observation, and that the 

 acoustical apparatus proper consists of a ganglion in the 



bladder wall, organised similarly to that in the Acridia. 

 In the normal condition, the otoliths are pressed by the 

 surrounding hair-tufts against the acoustical apparatus 

 only in the case of stronger sound-stimuli, and they have 

 then a damping action. 



NOTES FROM THE ''CHALLENGER" '^ 



pROF. THOMSON in this paper after briefly referring to a 

 •^ visit to the Hawaiian crater of Kilauea, proceeds as 

 follows : — 



In the section bstween Hawaii and Tahiti, except at one 

 station close to Tahiti, where the depth was 1,525 fathotns, the 

 depth ranged throughout the section from 2,000 to 3,000 fathoms 

 with a mean of about 2,600 fathoms, and the nature of the bottom 

 was very uniform. Except in the neighbourhood of the groups 

 of volcanic islands, where it was found to be largely composed 

 of volcanic de'dris and shore mud, it consisted mainly of red clay, 

 in many of the soundings containing a large admixture of the 

 decaying shells of Foraminifera, and in almost all including a 

 large proportion of manganese peroxide in the form of concre- 

 tions from the size of a nut to that of an OrbuUna, and passing 

 into fine, almost microscopic granules visible under a low power 

 in every sample of sounding. In two patches the siliceous 

 skeletons of Radiolarians were so abundant as almost to entitle 

 the deposit to the name of " Radiolarian ooze," and a patch 

 between these, nearly halfway between Hawaii and Tahiti, in its 

 abundance of surface Foraminifera approached a true "Globi- 

 gerina ooze." The larger samples of bottom brought up in the 

 dredge or trawl had of course generally the same character as the 

 contents of the "Bailie" sounding-tubes; but in these large 

 manganese concretions, up to the size of an orange, or even 

 larger, were collected in quantity, the greater part of the red" 

 clay being usually washed out. 



The surface-temperature naturally rose in passing southwards 

 from Hawaii towards the equator, and again sank from the equa- 

 torial belt towards Tahiti. The isothermobaths * between 14 C. 

 and 24° C. gathered together and approached much nearer to the 

 surface in the region of the trade-wmds, owing no doubt to the 

 rapid removal to the hot surface-water by evaporation and the 

 driving action of the wind. Thus the isotliermobathic line of 

 14° C, which is at a depth of 200 fathoms a little to the north 

 of Tahiti, is at a depth of 100 fathoms on the line. In the 

 Atlantic all the isothermobaths seem to participate in the rise in 

 the region of the trade-winds ; it is not so in the Pacific ; the 

 lines below 14° C. uniformly sink, forming a depression which 

 extends from lat. 10" N. to lat. 10* S, ; thus the isothermobath of 

 5° C, which may be taken as a type of these deeper lines, is 

 found in lat. 10° N. at a depth of 450 fathoms ; and in lat. 10° S. 

 at the same temperature within the limits of error of observation, 

 while in lat. 2° 34' N. it is found at 625 fathoms. The point 

 where the isothermobaths gather together most markedly and 

 approach nearest to the surface is a little to the north of the 

 northern boi-der of the equatorial counter current. This fall of 

 temperature is so decided as to indicate some special areas of 

 cold water ; and it may possibly be to some extent due to the 

 pressing up of deeper and therefore colder layers of the colder 

 trade-current against the hot stream. In the equatorial region 

 between lat. 10° N. and 10° S. there is a belt of water about 80 

 fathoms in thickness at a temperature generally over 25° C, and 

 the whole of this water, with the exception of the narrow band 

 of the counter current, is running to the westward at the rate of 

 from forty to seventy miles a day. 



The bottom fauna over the whole of the manganese area is- 

 very meagre, both as to number of species and number of indi- 

 viduals. 



After a week's stay at Tahiti the Challenger left the harbour' 

 of Papeete on the 3rd of October, and arrived at Valparaiso on 

 the 19th. 



' " Preliminary Report to the Hydrographer to the Admiralty, on some 

 of the Results of the Cruise of H.M.S. Challenger between Hawaii and' 

 Valparaiso," by Prof. Wyville Thomson, F.R.S., Director of the Civilian 

 Scientific Staff on board. Paper read before the Roval Society. 



2 The word Isotherm having been hitherto so specially appropriated to ' 

 lines passing through places of equal temperature on the surlace of the 

 earth, I have found it convenient, in considering these questions of ocean' 

 temperature, to use the terms Isothermobath and IsabathytheriH ; the 

 former to indicate a line drawn through points of equal temperature in a 

 vertical section, and the latter a line drawn through points of equal depth at 

 which a given temperature occurs. Isothermobaths are shown in a scheme 

 of a vertical section, such as Plate II. Isobathytherms are of courie pro-' 

 jected on the surface of the globe. . - 



