444 



NA TURE 



[March S, 1900 



It is obvious that the movements and other events to which 

 sun-spots are due would only need to become a good deal more 

 energetic to render our sun a perceptibly variable star with a 

 period of eleven years. Now, a cause which may perhaps 

 render them more effective is this. According as the sun or 

 other %\.-\x shrinks, its sun-spot or star-spot period will presum- 

 ably undergo some change ; but it is very unlikely that this 

 change will follow the same law as that which governs the pro- 

 gressive shortening of the period of natural pulsation within 

 the entire mass of the star. Accordingly, at a certain epoch 

 in the history of the star, the two periods may approximate to 

 one another. Thereupon the events producing star-spots are 

 likely to acquire augmented intensity, which may render the 

 star a variable star for a long cosmical period ; in fact, until 

 further shrinkage shall have slowly destroyed the adjustment. 



Nor is it necessary that the two periods— that of star-spot 

 frequency and that of natural pulsation within the star — sh<tll 

 become identical. The fluctuations in the number and size of 

 star-spots will probably become exaggerated whenever the two 

 periods in question become related in other simple numerical 

 ratios. Accordingly, a star in the whole course of its life-history 

 may at more than one stage become a variable star, although the 

 most conspicuous fluctuation of its brightness, and that which is 

 represented by the simplest form of light curve, ^ will only occur 

 when the periods become equal. 



In Messier V. — the great cluster in Virgo — the evidence which 

 is published by Piof. Bailey in the Astrophysial Journal oi last 

 November establishes the fact that at leabt forty of its stars, or 

 nearly one-twentieth part of all the stars of the cluster, differ but 

 little from one another in brightness, and exhibit other resem- 

 blances which indicate that these stars are now very much alike 

 in their physical condition. It is, therefore, in a considerable 

 degree probable that at a remote epoch in the past they were so 

 nearly in the same physical condition as to have then had pretty 

 nearly the same brightness, the same star-spot period, and the 

 same period of internal dynamical vibration. This amount of 

 resemblance between so large a proportion of the stars of the 

 cluster will not seem improbable to any one with experience of 

 the appearances of star clusters, in many of which a conspicuous 

 feature is the very notable propci'^ion of the stars which are of 

 one or of some few definite magnitudes. 



If then these forty stars were originally nearly alike, they 

 would continue so during their subsequent history. They would 

 all shrink in the same way, they would continue at each sub- 

 sequent epoch to have nearly the same star-spot period, and also 

 to have ail of them approximately the same period of natural 

 internal pulsation ; and would accordingly all arrive nearly 

 simultaneously at that stage when these periods approximate. 

 They would then all of them become variables, and under pre- 

 cisely the circumstances which have been observed, viz. with 

 the simplest form of light curve, and with some approach 

 towards having the same maximum of brightness, the same 

 minimum, and the same period of fluctuation. 



It has been observed above that in the successive adjustments 

 that may arise while a star is shrinking, some may be of a kind 

 to lead to variability with more than one minimum in each 

 cycle, while the principal adjustment (where the two periods 

 become the same and not merely simply related) will have only 

 one minimum in each cycle. Instances of both are presented 

 by known variable stars ; though naturally the second case is 

 that which has been most noticed because it is, when it occurs, 

 that the brightness of the star exhibits the most conspicuous 

 range of fluctuation. G. Johnstone Stoney. 



8 Upper Hornsey Rise, N., March i. 



A New Peripatus from New Zealand. 



As the genus Peripatus is always regarded with exceptional 

 interest by zoologists, I should like to make known through the 

 medium of your column's the discovery of a new and very 

 beautiful species in the dense beech forest at the head of Lake 

 Te Anau, in the South Island of New Zealand. I lound it a 

 few days ago in the decaying trunks of trees (presumably 

 beech), and have since collected between twenty and thirty 

 specimens. The species resembles the well-known P. novae- 

 zealandiae in shape and size, but is at once distinguished both 



1 There is quite enough of correspondence between the light curve of 

 those variable stars which have one nihiimum in each cjcle, and the curve 

 of sun-spot frequency, to cieate an appreciable presumption in favour of the 

 speculation of the present paper. 



from it and from the other New Zealand species, P. siiteri, by 

 the possession of only fourteen pairs of walking legs, and by the 

 presence on the dorsal surface of fifteen pairs of green spots 

 arranged segmentally, one pair over each pair of legs, and one 

 pair over the oral papilla. The general coloration of the dorsal 

 surface is dark grey mottled with orange, with a dark median 

 band and a black or nearly black triangular patch between 

 each two successive green spots on each side. There are also 

 pale orange or whitish papillae, very regularly arranged. The 

 ventral surface is mottled grey or violet, with pale areas between 

 the legs. The antennae are grey, ringed with orange. One 

 specimen is almost jet black on the dorsal surface except for 

 the green spots. Adult females are at once distinguished 

 by the presence of an elongated protuberance between 

 the legs of the last pair. This organ is yellowish in colour and 

 bears the genital aperture, closely resembling the ovipositor of 

 the egg-laying Victorian species, P. ovipariis. The males are 

 rather smaller than the females, and have a white papilla at 

 the base of each leg of the last nine pairs. I propose for this 

 species the name I'eripatus viridnnactilatus. 



Lake Te Anau, N.Z., January 14. Arthur Dendy. 



Notes on the Occurrence of Amphioxus at Singaprre. 



The following notes on the occurrence of Branchiostoma 

 behhe'-i, (Jray, at Singapore have been written at the suggestion 

 of Dr. Arthur Willey, who has kindly examined and identified 

 the specimens for me ; they were collected by Mr. W. F. 

 Lanchester and myself, and are, I believe, the first that have 

 been obtained from the locality. The first indication we had of 

 the presence of Amphioxus in the district occurred about the 

 middle of November 1898, when a number of young examples 

 were found amongst the material collected by tow-netting at the 

 extreme surface of the water about one or two hours after sunset. 

 At the time we were living on a small island about ten miles 

 off Singapore, and we tow-netted every night just outside or over 

 the edge of the reef surrounding the island. The tidal currents 

 were generally very strong, and no doubt brought a considerable 

 amount of the plankton from the deeper layers to the surface. 



651 h myotome. 



point where 

 56th myotome dilatation of 

 fin commences 



NO. 1584, VOL. 6l] 



Fig I. — Branchiostoma. helcheri, caudal extremity, before met.Tmorphosis; 



length of whole larva about 5 mm. 



a, Nerve cord ; b, notochord ; c, rectum ; d, ventral fin space. 



Up till the end of November (when we left the island) young 

 Amphioxus continued to be fairly plentiful ; but they were 

 never met with elsewhere, and in June last year I visited the 

 island again and could find no trace of them. 



All these specimens were in different later stages, some having 

 completed their metamorphosis, the fin-rays and ventral fin- 

 chambers being already formed, while in others the gill-slits 

 were still unilateral and opened freely to the exterior. 



After the capture of the above examples we repeatedly 

 dredged in the hope of obtaining adult examples, but on only 

 one occasion were we successful, and then only a single specimen 

 was found. It occurred in about six fathoms of water on a 

 bottom composed of somewhat coarse gravel-sand close to the 

 west entrance to Singapore Harbour. I am inclined to attribute 

 our failure iri securing more adults to the nature of the ground 

 in which they live. With an ordinary dredge they could easily 

 wriggle through the meshes, and the only time I tried a canvas- 

 bag dredge it filled so rapidly with sand as to be quite useless. 



