34? 



NA TURE 



[September 9, 1922 



the transmitted intensity depends almost entirely on 

 the ratio of the densities. If we take the case of a 

 partition of wood having a density half that of water, 

 calculation then shows that at normal incidence about 

 4 per cent, of the sound is transmitted if the thickness 

 be 1 cm. Reducing the thickness to 2 mm., the 

 intensity of the transmitted sound increases to 

 50 per cent., and rises to 80 per cent, if the thickness 

 is only 1 mm. 



What I desired to emphasise in my previous letter 

 is that the diminution in the sound transmitted with 

 increasing thickness is not necessarily due to any 

 absorption, but is explained by the effect of the 

 reflection at the second surface which, when the 

 thickness is small compared with the wave-length, 

 neutralises the reflection at the first surface. This 

 does not appear to be sufficiently appreciated, and 

 some of the conclusions drawn in Prof. Watson's 

 paper require correction accordingly. The effect of 

 the second surface is also of importance when total 

 reflection ought to take place according to the usual 

 formulae at the first surface. With a thickness less 

 than a wave-length, part of the sound is transmitted. 

 This case has been treated by Lord Rayleigh (" Col- 

 lected Works," vol. vi. p. 71). 



Arthur Schuster. 



The Annelids of Iceland and the Faroes. 



This is a subject about which very little has 

 hitherto been known. In discussing the part which 

 white ants play in the economy of nature Prof. 

 Henry Drummond compared them with earthworms. 

 He referred to Darwin, and said that in " Vegetable 

 Mould " a reference was made to the existence of 

 earthworms in Iceland. I cannot find any such 

 allusion. It is true that a few worms have been 

 recorded for Iceland and one for the Faroes. I am 

 fortunately in the position to add somewhat to our 

 knowledge. My son, Dr. J. Newton Friend, having 

 recently returned from an expedition in those islands, 

 I have had the privilege of examining his collection 

 of annelids. The following are the results : 



The common earthworm (Lumbricus terrestris, L.) 

 flourishes in Iceland. I examined twenty-three 

 specimens, twenty of which were perfectly adult. 

 Not one of them differed in any particular from the 

 type as found in England. I hoped to find sper- 

 matophores, but in this matter disappointment was 

 experienced. The specimens were collected near 

 Reikjavik at the beginning of August, and were just 

 in the right condition for laying their cocoons. 



The red earthworm (L. rubellus, Hoffm.) was also 

 found. Though adult it was smaller than our English 

 specimens usually are, and the dorsal surface was of 

 a darker brown colour. I have often found similar 

 specimens, however, in the British Isles, so that they 

 are in no sense to be looked upon as a variety. 



The purple worm (L. purpureus, Eisen = L. cas- 

 taneus, Sav.) has already been recorded, alike for 

 Iceland and the Faroes. Thus each of the three 

 common species of European Lumbrici is now known 

 to be a denizen of Iceland. To these may be added 

 two species of the genus Dendrobaena. One of these 

 (D. rubida, Sav.) is best known by the variety 

 usually named the gilt-tail, a denizen of ripe manure 

 and decaying leaves. The other (D. octoedra, Sav.), 

 although widely distributed geographically, is not a 

 common species in Great Britain. Up till the present, 

 then, five species only of the Lumbricidae have been 

 recorded. 



The shores of Iceland, if they could be worked as 

 Claparede worked the Hebrides, would doubtless 

 yield a variety of forms, especially the red-blooded 

 pot-worms or pachydrilids. None of these, so far 



NO. 2758, VOL. I IO] 



as I am aware, has been up till the present placed 

 on record, but Clitellio arenarius, O. F. M., well 

 known on our English coasts, is reported for the 

 coasts of Iceland. 



I can find no records for the Faroes except the 

 purple worm already noted. It is, therefore, with 

 peculiar pleasure that I am able to add two new 

 members to the list. These are both enchytraeids, 

 and were collected in peaty earth near a stream 

 some two miles inland from Thorshaven. One of 

 these was a pachydrilid (Lumbricillus lineatiis, 

 O. F. M.). I have written fully on the synonymy 

 in the Irish Naturalist, and my conclusions are 

 supported by the more recent investigations of the 

 American helminthologist, Welch. 



The other enchytraeid is of the white-blooded 

 kind (Mesenchvtraeus oligosetosus, Friend). It was 

 found some time ago among gleanings made in Jersey, 

 and described by me in the Zoologist. I have more 

 recently found a striking variety of this worm, or 

 an allied species, near Birmingham. The Faroes 

 material agreed with the Jersey. The worm is about 

 a third of an inch in length, and belongs to the group 

 which has enlarged setae on the segments which 

 contain the spermathecae. It may also be noted 

 that I found one of the commoner opalines parasitic 

 in the Faroese enchytraeids. Our list therefore 

 stands thus : Mesenchytraeus oligosetosus, Faroe Is. ; 

 Lumbricillus hnealus, Faroes ; Clitellio arenarius , 

 Iceland ; Dendrobaena rubida, Iceland ; Dendrobaena 

 octoedra, Iceland ; Lumbricus purpureus, Faroes and 

 Iceland ; Lumbricus rubellus, Iceland ; Lumbricus 

 U 1 1 1 •■Iris, Iceland. 



Addendum (Aug. 16). — A further investigation with 

 pocket lens has resulted in some interesting additions 

 to the foregoing list : 



Achaeta minima Southern, only 1 mm. in length, 

 but agreeing exactly in all particulars with the 

 material from Ireland. The intestine contained 

 peaty soil with a number of diatoms. 



Marionina (Chamaedrilus) sphagnetorum (Vejd.j. — 

 Very slender, but true to type. White (colourless) 

 blood. I stated my reasons in these columns some time 

 ago for transferring this species to the genus Chamae- 

 drilus. 



Dorylaimus obtusicaudatus Bastian. A fine female 

 nematode, about z\ mm. long. All from the Faroes. 

 Hilderic Friend. 



Cathay, Solihull. 



On the Reality of Nerve-Energy. 



The expression " nerve-energy " is widely used 

 both by non-technical writers and by medical and 

 physiological authors as well. 



What the former mean by it is of no particular 

 moment ; but in medical and physiological literature 

 it should connote something quite definite, if indeed 

 the existence of nerve-energy is admitted at all. 

 There seems a doubt whether its existence is to be 

 admitted in a formal sense, for although certain 

 physiologists use the expression nerve-energy as a 

 convenient term, the thing itself is not discussed in 

 their text-books, nor does it find a place in the 

 indexes. 



If nerve-energy has no place in the scheme of things 

 vital as conceived by modern physiologists, then the 

 term ought not to be used by them just because it is 

 occasionally a very useful one. When they do use it, 

 it means no more than " innervation." 



The subject is full of difficulties, one of which is 

 our having to reckon with the use of the still vaguer 



