January i, 1920] 



NATURE 



435 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of. rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



Atomic Energy. 



Referring to the notice of my recent Trueman 

 Wood lecture on p. 420 of Nature of December 25 

 last, let me explain that I admitted that we could 

 not .-It present tap or utilise intra-atomic energy except 

 what is given us spontaneously. But we may claim 

 to be utilising intra-atomic properties, since without 

 some kind of disintegration the right kind of pro- 

 jectiles would not be available. I say clearly in the 

 lecture " it is atomic properties rather than atomic 

 energy that are at present being utilised" in wireless 

 telephony. 



Furthermore, although the excitation of healthy 

 retinal nerves is primarilv dependent on the energy 

 of incident light, vet the action is as if the atoms of 

 a retinal substance acted as accumulators, storing up 

 an Jether disturbance of quite unphysiological fre- 

 quency until a quantum has been collected, when a 

 stimulating projectile is liberated. If anything like 

 this happens, the energy actually utilised is atomic 

 energy; for if that had no existence, the light-waves 

 would be powerless. There may be pathological cases 

 where optic-nerve stimulus is independent of received 

 luminous energy but that is a highly undesirable state 

 of affairs. Oliver J. Lodge. 



Metamorphosis of AxolotI caused by Thyroid-feeding. 



The fact that a diet of mammalian thyroid will 

 induce frog-tadpoles to metamorphose precociously 

 into the adult form is now well established. Tt is of 

 some interest to find that this diet produces a similar 

 effect in a form which usually does not metamorphose 

 —the .AxolotI. This is the larva of a salamander 

 known as .Amblvstoma, but is remarkable in being 

 neotenic, i.e. it normally fails to metamorphose, and 

 attains full size and sexual maturity while keeping its 

 larval characters. Chief among these are the external 

 gills and the fin along the back and both borders of 

 the tail but the adult also differs from the larva in 

 colour, "in shane of head, in the development of eyes 

 and eyelids, in the rounded fonn of the tail, and, of 

 course, in the use of its limbs for progression on 



land. ,„ . , , TI7- 



Marie von Chauvin in Germany (Zettschr. f. Wtss. 

 ZooL. vol. xxvii., 1877, and vol. xli., i8S,) and R- <"'• 

 Boulenger in this country (Proc. Zool. Soc, iqi.^ (2)) 

 have succeeded in gettine .\xolotls to as.sume the 

 adult form by forcing them to breathe air, either by 

 keeping therh in damp moss or in a gradually 

 diminishing quantity of shallow water. 



In conjunction with Mr. D. F. Lenev, I have been 

 trying the effect of thyroid diet on .Axolotls. Two 

 vouns' soecimens. n-; cm. and 12-7 cm. long, and 

 therefore presumably between six and twelve months 

 old were kept in a tank at an average temperature 

 „f ',-°-i6° C. in a deoth of water (more than 2 in.) 

 considerably I'reater than that needed to induce air- 

 bre.ithint^. They were fed on ox thyroid, at first 

 three times, and later twice, a week. 



The thyroid diet be&;m . on November ^o last. On 

 December 15 distinct alterations were visible in colour 

 and in resorption of gills and fin, and on December 17 

 the stage which is critical in metamorphosis mduced 

 bv air-breathinc (see Boulenger's caper) had been 

 passed, the animals being in Boulenger's stage 6, 



NO. 2618, VOL. 104] 



with only vestiges of gills and fin. On December 19 

 the next or penultimate stage, with scarcely a trace of 

 larval characters, was reached. The larger specimen, 

 the metamorphosis of which was slightly more 

 advanced, had climbed out of the water up .a plat- 

 form provided for the purpose, and its skin was as 

 dry as an ordinary salamander's. When placed on 

 the table they both walked well, thus differing 

 markedly from the larva, which cannot use its legs 

 efficiently if placed on land. Curiously enough, on 

 the succeeding day the larger animal had returned to 

 the water, where it remained until December 23. It 

 then again left the water of its own accord, and up 

 to the time of writing (December 24) has remained 

 in air. Two other specimens of similar size, fed on 

 worms and kept in shallow water, according to 

 Boulenger's method, have, so far shown only minimal 

 changes. 



Two points are of special interest. First, the time 

 of metamorphosis — just over three weeks — is much 

 shorter than anv previously recorded. Boulenger's 

 larvic took from twelve to .sixteen weeks, Marie von 

 Chauvin 's from seven to forty weeks. Secondly, the 

 "critical stage" in the metamorphosis was reached 

 apparently without the animals breathing air at all; 

 i.e. two entirely different causes, forced air-breathing 

 and a thvroid ' diet, can produce the 'same result — 

 metamorphosis. It was not until December iq that 

 they were observed to come to the surface for air;_ and 

 even after that, although possessing no functional 

 gills, thev spent much time at the bottom of the 

 water, onlv occasionally rising to float suspended close 

 below" the surface with limbs outspread, after the 

 fashion of newts. 



Many interesting problems present themselves, which 

 it is hoped to work out .is opportunity offers. Mean- 

 while, this note is oublished in the hope that others 

 who possess .\xolot1s will repeat and develop experi- 

 ments along these lines. I should be sjlad to enter 

 into correspondence with anvone intending to work 

 on the subject, with the view of preventing useless 

 overlapping in the working out of the problems that 

 arise ; and, further, I should be very grateful if anvone 

 possessing Axolotls, whether young or old, would give 

 me the opportunity of purchasing some, as they are 

 at present very difficult to obtain in the market. 



Julian S. Huxley. 

 New College, Oxford, December 24. 



The Hibernation of the House-fly. 



M. DE Seguy's discovery of larvae of Musca domes- 

 lica in the bodies of snails. Dr. J. C. Gahan's ob- 

 servations thereon in the Times, and the note in 

 N.\ture of December 18 last are very interesting to 

 biologists, but it is most improbable that a winter 

 crusade against the Helicidas would have any appre- 

 ciable effect in diminishing the summer swarms of 

 flies. , 



I am led to this conclusion by circumstances under 

 my immediate observation. Round my house is a 

 large flower-garden in which I work constantly- at 

 all seasons, desperately worried in summer by legions 

 of house-flies. In the course of forty years I have 

 never come across one of the larger Helicidae m this 

 garden; and mv head gardener, a very intelligent 

 man and a goocl observer, assures me that in thirty 

 years he has never seen one in the kitchen-garden, 

 which is distant half a mile from the flower-garden. 

 Slugs abound in both, but the only one of the Helicidae 

 that is found is a very small snecies with a thin, 

 flattened shell (? Helix cellaria. Miiller) and a body 

 too small to accommodate the larva of a house-fly. 

 It is also the reverse of abundant. There must, 



