Nature Vol. 27I 26 January I978 305 tributions correspond to a range of temperatures from 5.2 to 6.3 keY, The blind of Persia in excellent agreement with the pre­ dicted thermonuclear value of 5 keY. THE no.te published in News and habitat •is concerned. The only sound Views (264, 113; 1976) on the blind hypothe~is about regres~ed fishes cave fishes of Persia mentioned the found in wells and other artificial discovery of the two cavern:icolous water outlets is that these forms nor­ forms Noemachilus smithi (Cobitidae) maHy Hve in the phreatic sheets and and Iranocypris typhlops (Cyprinidae) are occasionaHy attracted to zones in the same well-like outlet. This is of exposed to light by organic remnants The prevalence great interest for the :wogeographical of or humarn origin. The fact and etho-ecological interpre,ta.tion of tha.t fishes of the same are of chaos the possible mechanisms which led somet!limes observed in wells separated from N. MacDonald epigean fishes to colonise subter­ by a grea.t distance is, in my opinion, ranean waters and evolve under­ the stmng.est argument in favour of IT has been known since the time of ground into ·isolated homogeneous this view. Mees r·eported the piiesence Poincare that quite simple conservative populations composed entirely of eye­ of the free"swimming Milyeringa in dynamical systems, such as two coupled less and depigmented individuals. only two of the three wells he vi~ited linear oscillators, can exhibit highly These phenomena of regressive evolu­ (Milyering, Kudmurra and Tanda­ complicated behaviour. As well as tion have been well studied on several biddi, the last halfway between and periodic trajectories, which are closed populations inhabiting caves (Thines some 10 mi•!.es from the other two), curves in phase space, there are also L'evolution regressive des Poissons whereas the ed-like Anommato­ trajectories which, loosely speaking, cavernicoles et abyssaux, Masson, phasma was found in a•ll thre\! sites. fill up volumes in phase space. The Paris, 1969), but little, if any, specific The cases of Iranocypris typhlops and rather special nature of conservative attention has been given to the case of Noemachilus smithi seem similar systems limits the number of physical of cavernicolous forms found in wells to that of Milyeringa veritas. The contexts in which this behaviour can and artificial outlets. It is therefore ecological conditions in which these be manifested. (For some interesting fortuna,t'e that Mr Smith was able to fishes live a:r.e mor.eover similar to examples see Henan & Heiles Astr. J. discover this new Noemachilus form those repor;ted as early as 1904 by 69, 73; 1964; Dunnett, Laing & Taylor in associa·tion with the pr•eviously dis­ Goeldi for J. math. Phys. 9, 1819; 1968.) Analo­ covered lranocypris (Brunn & Kaiser (Goeldi Rept. 6th Int. Zoo!. Congr. gous behaviour has been observed in Dan. Scient. Invest. Iran, Munks­ Bern, 549; 1904), a very peculiar cat­ recent years in a number of nonlinear gaard, Copenhagen, 1943). However, bdongi,ng to the family Tricho­ models of physical systems which are the coexistence of two distinct re­ mycte•ridae which he found in a open or dissipative, rather than con­ gressed speci,es in the same well has cistern of Marajo Island in .the mouth servative. This is leading to reappraisal been observed before. In 1962, Mees of the Ama:wn ahd which was re­ of our understanding of these systems. found two diff,enent blind and depi.g­ discovered recently (Delamare, per­ The best known example is that put mented Teleosts, Milyeringa veritas sonal communication). I have col­ forward by E. N. Lorenz (J. atmos. (Gobiidae) and Anommatophasma lected specimens of the blind Clariidae Sci. 20, 130; 1963). He starts from the candidum (Synbranchidae) in two Uegitglanis zammaranoi in the carnal­ partial differential equations for flow wells depending on the same subter­ isations of the Iscia-Ba•idoa pumping in a layer of liquid of uniform depth ranean system and located about 10 station (SomaJ,iland) some 60 miles with a constant temperature difference miles apa•rt, near Ya,rdee Creek Sta­ from the wen of Uegit, wher·e the first maintained between the upper and tion, North West Cape, Australia specimens were discovered in 1923 by lower surfaces. These have a steady (Mees J. R. Soc. West. Austr. 45, (1), Gianferrari (Atti. Soc. Ita!. Sc. Nat. state solution with zero flow. As the 24; 1962). Mus. Civ. Star. Nat. Milano, 62; temperature difference is raised this The coexistence of disti•nct caverni­ 1923). To .the present day, 1this dis­ solution becomes unstable and convec­ colous forms in a same biotope other tance is by far the greatest to have tive flow solutions replace it. Lorenz than a cave, raises the question of the been reported for the geographical examines one particular mode of con­ exact nature and .extent of their extension of a cavernicolous fish mot vective flow, and uses a truncated habita,t. Underground wat:ers can be dwelling in a cave (Thines Rev. Zoo!. Fourier expansion to reduce the prob­ traced with sufficient precision in Bot. A/ric. 57, 117; 1958). The case lem to one involving three coupled many karstic systems (the system of of Noemachilus smithi can thus be ordinary differential equations. The sinks, underground caverns and considered as a typical .ins.tanc•e of an variables are the intensity of convective streams found in limestone areas), already well -known ,phenomenon, flow, the temperature difference be­ whereas water sheets fe,eding wells or whose meaning for biospdeological tween ascending and descending cur­ pumping sites do not lend themselves research is clear. rents, and a quantity measuring the to simila·r descriptions. In addition, departure from linearity of the such phreatic water tables cannot be G. TRINES temperature gradient across the fluid explored by speleologists, so that the layer. Lorenz finds a second instability, only topogra.phical data are thos•e CPEC Animal Behaviour, beyond which the simple smooth con­ furnished by geological surveys. Thus, Louvain University vective flow is replaced by an ex­ biospeleologists have had to limit 304I Pellenberg tremely complex and unpredictable themselves to 'inference as far as the Belgium flow. The mathematics of this situation have become popular in the past few years, and progress in understanding on turbulence held at Berkeley in 1975 pointed out (Phys. Lett. 53A, 77; 1975) the nature of the complex flow is re­ (Springer Lecture Notes in Mathe­ a remarkable parallel between the viewed in the proceedings of a seminar matics No. 615; 1977.) Lorenz model and a classical approxi­ The conditions for this new insta­ mation to the dynamics of a single N. MacDonald is in the Department of Natural Philosophy in the University of bility are physically unattainable in this mode laser. In this case the three vari­ Glasgow. experiment. However, H. Haken has ables are the field strength and polar-

Q Macmillan Journals Lt