;i2 



NA TURE 



[March 28, 1S95 



correlated with the large amDunt of wear and tear en- 

 tailed by the constant " scrapinj " of birnicles, S:c. This 

 appears to be confirmsd by compirison with Hclcion, 

 ia which Ltminiria constitutes the chief, if not the only, 

 fojd, and in which the radula is relatively somewhat 

 shorter. 



At Granton, in July, the larger limpets appeared to 

 feed most frequently ; but at Aberystwyth, during the 

 colder months, the small individuals are far more active. 

 Sheltered corners and warm days afford the best chance 

 of watching the movements. Though limpets undoubtedly 

 regain their scars, or secure places, as the tide advances, 

 I am inclined to think they must also often feed when 

 covered by the water, for (i) the finest specimens are 

 found low down, and their time for feeding when un- 

 covered is limited ; (2) I have seen a small limpet feed 

 on Corallina in a tide-pool. 



The scraping sound heard on the rocks during warm 

 weather is not entirely due to feeding limpets. Purpura 

 lapillus is also busy at work " sawing out " balani from 

 their shells. 



LocalitytSensc. — I still think./^ja* Prof. Lloyd Morgan, 

 that the head-tentacles are not indispensable to homing, 

 though it must be admitted that they may commonly 

 help in the process. One limpet observed homing by me, 

 certainly seemed to be " feeling '' its way along by means 

 of these organs, which were extended and waved about 

 and applied to the rock from time to time, not by the 

 e.xtreme tip only, but also laterally for about ,',. ot an 

 inch from this. This individual was No 2 of a small 

 group living among the barnacles, and kept under 

 observation from November 26 till the present time. 

 The dimensions of these limpets are as follows: — No. 

 1, 5" X i"; No. 2, ditto; No, 3, t" X § " ; No. 4, 



rfr" X T; No- 5. ii' X 



On November 2S, at 



3.15 p.m., I found -No. 2 leeding iV' from its scar. 

 About half of each tentacle was excised (i.e. the part 

 previously noticed "feeling"), and the animal was re- 

 placed where found. On November 29, at 2.55 p.m., it 

 was found back on its scar. A similar operation was 

 performed on No. 5, found feeding 2'," from its scar, on 

 December 12, at 3.15 p.m. On my next visit, at 2.55 

 p.m. on December 14, the animal was found to have 

 regained its scar, which, by-theby, is permanently 

 submerged, being in a small tide-pool. It is true the 

 tentacles were not entirely removed, as was the case 

 with the two Granton limpets which homed after excision. 

 It now appears to me probable that the mantle-lcnlaclcs 

 may help m homing. These are small conical structures 

 lodged in pits in the mantle edge (Harvey Gibson, 

 Trans. R.S. Edin. 1885), and capable of retraction and 

 extension. About 100 of them are present. In sub- 

 merged limpets I have seen these tentacles protruded 

 for about ,',./' beyond the margin of the shell, and executing 

 active " feeling ' movements. These were particularly 

 noticeable in an individual which, having regained its 

 scar wrong end on, was shuftling round into the right 

 position. When the front end of the limpet came to point 

 in the right direction, one side of the shell was lowered, 

 and the mantle-tentacles on that side were withdrawn ; 

 the same events then happened on the other side. 

 These tentacles appeared to be of two kinds, longer and 

 shorter, the latter being two or three times as numerous. 

 Prof. Herdman first suggested to me that the mantle- 

 tentacles might have to do with the locality-sense, and 

 It at any rate appears probable that they are concerned 

 with accurate adjustment on the scar. It is worth 

 noting that very small limpets home as well as large 

 ones, e.g. No. 5 above, and much smaller ones which 

 have fallen under my notice. Prof. Lloyd Morgan's 

 observations, so far as they refer to knowledge of local 

 surroundings which limpets possess, are confirmed by an 

 experiment mide on No. 1. On December 16, at 4.5 p.m., 

 thisanimil was basy scraping barnacles 3' west of its 



NO. 1326. VOL. 51] 



scar. It was removed and placed 10 inches from home, 

 near the top of a nearly vertical barnacled surface (on 

 which it had been seen feeding at 3,15 p.m., November 

 28), which rises north of its scar. The next visit was 

 deferred till December 26, 12.25 P-ni., when the limpet 

 was at home. 



The homing faculty is not confined to Patella., but is 

 also possessed by Helcion peltucidum. This fact is new, 

 so far as I am aware. The animal in question eats out 

 a sheltered home in the bulb, or more rarely in the stalk 

 of Laininaria, and wanders out from this along the 

 thallus, rasping a " track " as it goes. I found, for 

 example, one individual at the end of an "eaten road " 

 3 inches long, and at the other end a very snug dwelling- 

 place drilled out in the side of the stalk. Helcion 

 mostly feeds under water. Like Patella, it possesses 

 mantle- as well as head-tentacles. 



The object of homing appears to be protection from 

 the assaults of the incoming or outgoing tide. There is 

 no danger when the animals are completely covered or 

 uncovered. In many cases the barnacles would other- 

 wise completely cover the rock, and afford \ery insecure 

 foothold. Once washed loose, a limpet presents a very 

 large surface liable to injury, unlike its neighbour Pur- 

 pura lapillus, which, withdrawn into its thick operculated 

 shell, can stand a good deal of knocking about. The force 

 with which limpets adhere is illustrated by the fact that 

 the five small limpets to which allusion has been made 

 were quite uninjured by the terrible gale and high sea of 

 December 21 and 22, to which they v>ere fully exposed. 

 The much thinner shell of Helcion is explained by the 

 sheltered position of its home. The depressed conical 

 shape of a limpet-shell is probably better fitted than any 

 other to resist the waves, but this statement is made 

 under correction. 



Formation of, and Adhesion to. Scars. — An'examination 

 of the 'tween-tide rocks at Aberystwyth w'ould readily 

 convince the most sceptical as to the power which 

 Patella possesses of excavating depressed scars. Lim- 

 pets are able to adhere very tightly to a smooth sur- 

 face which is much smaller than the foot, and by exam- 

 ination of such cases, and of specimens allowed to fix 

 themselves to a piece of plate-glass, I have come to the 

 conclusion that fixation is neither due to secretion of a 

 glutinous substance, nor to the formation of a vacuum 

 under the foot. It appears, in fact, to be a case of 

 " adhesion," like that between two smooth glass surfaces 

 brought very close together. The muscular foot is, so 

 to speak, rolled out on the rock, with which it is thus 

 brought into close contact. Prof. .Michael Foster sug- 

 gested to me the possibility of this method of explanation, 

 which is most probably the correct one. 



J. R. AlNSWOKTH D.wis. 



TERRESTRIAL HELIUM (.?). 



WE have received the following statement from Prof. 

 Ramsay : — 



" I have been trying for clues to compounds of argon. 

 Mr. Miers, of the IJritish Museum, called my attention 

 to Hillebrand's paper on Cleveitc, a rare Norwegian 

 mineral, which Ilillebrand said gave off 2 percent, of 

 nitrogen on warming with weak sulphuric acid. Cleveite 

 consists chielly of uranate of lead, with rare earths. My 

 idea was, if the so-called nitrogen turned out to be 

 argon, to try if uranium could be induced to combine 

 with argon. 



" The gas, on sparking with oxygen in presence of soda 

 loses a trace of nitrogen, probably introduced during its 

 extraction ; the residue consists of a mixture of .Argon 

 and Helium ! The brilliant yellow line, of which Mr 

 Crookes makes the wave-length 58749, is identical with 

 the Helium line. I am collecting the gas, and shall 

 shortly publish regarding its properlies."^ 



