382 



NA 7 URE 



[MaV 27, ly( 9 



4 inches gave perfect signals from Elmer's End, and no 

 disturbance. 



Case 3. — On shortening the distant wave-length still 

 more, so as to make it 450 metres, the neighbouring station 

 could not be completely cut out without at the same time 

 introducing a trace of superposed disturbance into the 

 messages received from the distant station. 



Case 4. — The difference of wave-length between the two 

 stations was now, therefore, again slightly increased, the 

 Elmer's End wave-length being adjusted to 480 metres, 

 wiih the local station still remaining at 300. 



In this case perfect and strong signals could be received 

 from Elmer's End again, but the separation of the in- 

 ductive connection had to be as much as 6 inches in order 

 completely to cut out the local signals from the neighbour- 

 ing station. 



it follows, therefore, that when two powerful stations 

 are so excessively near each other as they were in this 

 case— namely, in adjoining fields— a distant signal can 

 be heard with perfect clearness, i.e. without any trace of 

 disturbance, only when its wave-length is more than half 

 as great again as that of the neighbouring station; but 

 that undisturbed signalling is much more easy when it 

 approaches double that magnitude, or, of course, when the 

 neighbouring stations are not quite so close together. 



In no case was any trace of harmonic detected ; e.g. 

 when a station was sending 300 metres, and the neigh- 

 bouring receiving station _ was attuned to 600 metres, it 

 did not necessarily feel any disturbance. The waves 

 emitted and received by these radiators appear to be prac- 

 tically pure. Oliver Lodge. 



Jl 



MARINE BIOLOGY IN THE TORTUGAS.' 

 ^HE volumes referred to below contain a series of nine- 

 teen papers based on work done or material collected 

 at the Marine Biological Laboratory of the Carnegie 

 Institution, situated on Loggerhead Key, olT the south- 

 west coast of Florida. The observations recorded bear 

 ample testimony to the exceptionally favourable situation 

 of the laboratory for the prosecution of marine biological 

 research, and also to the facilities afforded on a liberal 

 scale for work on a wide variety of subjects. 



Dr. A. G. Mayer, the director of the laboratory, describes 

 the annual breeding swarm of the Atlantic palolo {Eunice 

 fucata, Ehlers), which occurs within three days of the day 

 of the last quarter of the moon between June sg and 

 July 28. The worm when mature (and immature worms 

 take no part in the swarming) is about 10 inches long 

 and Its sexual products are limited to its posterior half. 

 Before sunrise on the day of the annual breeding swarm 

 the worm crawls out backwards from its burrow in the 

 coral or limestone rock until the whole of the sexual por- 

 tion IS protruded. By means of vigorous twisting move- 

 ments this portion is detached, swims vertically upwards 

 to the surface of the water, and there continues to swim 

 about with Its posterior end in front. These sexual por- 

 tions of the worms, which show no tendency to congregate 

 are present in great abundance at Tortugas, scarcely a 

 square foot of the surface above the coral reefs being free 

 from them. At sunrise the worms undergo violent con- 

 tractions, which cause the expulsion of the sexual products 

 through rents or tears which are formed in the body wall • 

 the torn and shrivelled remains of the body wall then sink 

 down to the bottom and die. Although light is probably 

 a contributory cause, it is not the sole cause of this spasm 

 of contraction, which takes place, though it is somewhat 

 delayed, in swimming worms which have been removed 

 to a dark room. After casting off its posterior sexual seg- 

 ments the anterior part of the worm crawls back into its 

 burrow, and regenerates a new sexual end. The author 

 h.is attempted to determine the nature of the stimulus to 

 which the worm responds when it swarms, and he shows 

 that the worms never swarm when moonlight is prevented 

 from falling upon the rocks in which thev are ensconced. 

 J ho paper is a most interesting contribution to the study 

 ot this remarkable phenomenon. 



•W«v''T "■"■""I 'h^ .Torengas Laboratory of the Carnegie In.tuntl n of 



Dr. Mayer describes a series of experiments on the 

 scyphomedusan Cassiopca xamachana, from which he con- 

 cludes that the stimulus which causes pulsation is due to 

 the constant formation of sodium oxalate in the terminal 

 endoderm cells of the marginal sense organs. The sodium 

 oxalate precipitates calcium as calcium oxalate, thus 

 setting free sodium chloride, which he shows acts as a 

 nervous and muscular stimulant. Pulsation is thus caused 

 by the constant maintenance at the nervous centres in the 

 sense organs of a slight excess of sodium over and above 

 that found in the surrounding sea-water. 



The late Prof. W. K. Brooks and Mr. B. McGlonc have 

 studied the origin of the lung of Ampullaria. They find 

 that the gills, the lung, and the osphradium arise simul- 

 taneously, or nearly so, that they are developed from a 

 ridge or thickening of the mantle, and that they should 

 therefore be regarded as a series of homologous organs 

 specialised among themselves in different directions. The 

 lung becomes functional before the gill, as is shown by 

 the fact that the newly hatched young quickly die if they 

 are prevented from leaving the water, while adults can 

 survive an immersion of a month or more. Other papers, 

 the last productions of the late Prof. Brooks, contain a 

 discussion of the subgenus Cyclosalpa, a description of 

 the rare Salpa floridana (Apstein), and of a new appendi- 

 cularian — Oikoplcura tortiigensis — to the tail of some of 

 which a new species of Gromia was found attached. 



Prof. Reighard discusses the significance of the con- 

 spicuousness of the coral-reef fishes of the Tortugas. He 

 concludes, as the result of a long series of ingenious ex- 

 periments, that the coral-reef fishes do not possess that 

 combination of conspicuousness, with unpleasant attributes, 

 necessary to the theory of warning coloration. The con- 

 spicuousness of these fishes, since it is not a secondary 

 sexual character and has no necessary meaning for pro- 

 tection, aggression, or as warning, is without biological 

 significance. These fishes have no need of either aggressive 

 inconspicuousness, because they feed chiefly on fixed in- 

 vertebrates, or of protective inconspicuousness, for they are 

 afforded abundant protection by the reefs and their own 

 agility. Selection has therefore not acted on their colours 

 or other conspicuous characters, but these have developed, 

 unchecked by selection, through internal forces. An 

 attempt is made to apply this conclusion to the " warning 

 coloration " of conspicuous insects. 



There are other memoirs on the formation of chromo- 

 somes in various echinoderm ova; on the spermatogenesis 

 of the " walking-stick '* phasmid, .4pJopus niayeri, in which 

 the history of the accessory chromosome is traced and its 

 probable significance as a sex determinant discussed ; on 

 the habits and reactions of the crab Ocypoda aretiaria, of 

 Aplopus, and of the woody and sooty terns ; on the early 

 development of the scyphozoon Linerges, on actinian larvse 

 referable to the genera Zoanthella and Zoanthina ; on the 

 rate of regeperation in Cassiopea ; on regeneration of 

 the chelae of Portunus, on the life-history of the booby and 

 man-o'-war bird, and on the cestodes of the Tortugas. 



NO. 2065, VOL. 80] 



THE RELEVANCE OF MATHEMATICS. 

 /^NE of the most important achievements of the thought 

 -^ of the last fifty years has been the conclusive proof 

 of the logical nature of all mathematical conceptions and 

 methods, in opposition to Kant's view that mathematical 

 reasoning is not strictly formal, but always uses a priori 

 intuitions of space and time. This does not, of course, 

 imply that the methods of investigation followed by in- 

 dividual mathematicians are essentially different from 

 those followed by other inquirers, the objects of whose 

 researches are not purely logical ; it is well known, in 

 fact, that, though a proposition A may logically imply a 

 proposition B, yet B mav be deduced from .'\ by con- 

 siderations quite outside those of logic. Thus the exist- 

 ence of the solution of a certain important and famous 

 mathematical problem — known as " Dirichlet's principle " 

 — was, we may say, felt, and actually applied in domains 

 of pure mathematics, for certain physical reasons con- 

 nected with the equilibrium of statical electricity long 

 before rigorous logical methods were discovered for proving 

 the existence in question. The fact that propositions are 



