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illustrated with fine photographs from the author's ownresearches, which have been amongst the most finishedin the field . The Marconi Company's experimental radarequipment is in fact so excellent that Eastwood seems un-aware that much of the equipment used by other biolog-ists has been operated very inefficiently . He is over-optimistic, for example, about the general prospects fordetecting distant, low-flying birds . This problem hasnever been discussed adequately in print, because defenceestablishments are naturally secretive about the effective-ness of their low-altitude cover. However it is ornitholog-ically fortunate that most radars are not too sensitiveat low altitudes ; otherwise bats by .night, and swallowsand gulls by day, would have been more of a nuisancethan they are.

The remainder of the book surveys applications ofradar techniques to ornithology ; its only importantomission is reference to Lanyon's use (Natural History,1962 :18) of a police-type radar system to measure speedsof flight . These chapters comprise a genial summary ofother men's conclusions, rather than a critical appraisal ;the only hint of a biological controversy appears in thediscussion of whether migrants are drifted sideways bycross-winds . Yet the fact that this simple question-thefirst to be seriously investigated 11 years ago-remainsin dispute indicates that there are serious difficulties ofinterpretation. Radar has enormously increased ourknowledge of the natural history of bird migration, butmost radar systems detect birds en masse ; extractinginformation about the important biological questions-the behaviour of individual birds and its ecologicalfunctions-raises problems which are conceptual andbiological rather than technological in nature . At theleast, they demand sophisticated statistical methods,which to be effective require automated data acquisitionsystems. Better still would be specially designed radarsystems for monitoring single birds . Both solutions seemout of the question on present-day research budgets-and will probably remain so, until a Concorde collideswith a swallow .

I. C. T. NISBET

Chemistry of Learning. Edited by W, C . CORNING andS. C. RATNER . New York : Plenum Press (1967) .This is a book by the flatworm people . The rest of us

students of animal learning should read and if possibledigest it whether or not we are personally disposed toregard the worm runners as operators on the lunaticfringes . The book covers the proceedings of a symposiumheld in Michigan in September 1966. It contains twenty-six articles that range from an account c f regenerationto a `brief survey of possible mechanisms in informationprocessing' . There are papers on learning and lesions inants and on the behaviour of Hydra . And a great deal ofdetailed information about the performance of planar-ians, which is why the rest of us, who don't know ourway around the flatworm literature, should at least skimthrough the book to see the sort of information that isnowadays available .

That the flatworm stuff has been discredited, that theydon't show associative learning or chemical transfer, thatit has been largely an ill-timed attempt to jump on thenucleic acid bandwagon is now all part of the conven-tional wisdom, and it is only partly true . But conventionalwisdom is a convenient screen . One can use it to obscureone's own laziness from oneself or as an excuse to stick

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to views that one formed five or ten years ago, confidentin the knowledge that most of one's colleagues havesimilarly pigeonholed their opinions on the subjectand are equally reluctant to reopen and reassess the file.There is little doubt, even if one looks only superficiallyat the history of the case, that the worm runners madetactical errors in their presentation, methodologicalerrors in their experiments and some of them were justplain stupid in their willingness to throw away much wellestablished neurophysiology at a stage where they reallyhad very little to offer in its place. There were some prettywild statements about coding in long-chain moleculesand the role of RNA in learning . But most of this is pastand the same people, startled by the reaction of theinsulted establishment and now detectably paranoic,have gone back and begun to do the job properly .

The present generation of experiments does includethe controls known or believed to be necessary, andobservation of behaviour outside the immediate require-ments of scoring the expected responses . Some of thesources of variability are understood ; there are circum-stances under which planarians won't learn just as thereare conditions in which they quite certainly do . Muchof the apparent disagreement about performance resolvesitself once it is realized, for example, that planariansbehave quite differently in clean dishes and in well useddishes 'slimed' by naive animals before training is begun ;they learn much more slowly and sometimes not at allin the former. It is now accepted, moreover, that pasthistory matters ; the stage of regeneration, the sexualcondition of the worms, daily and lunar cycles all affectperformance, so that comparisons have to be made warily,since in most reports all these details are omitted . Won-drous though it may appear to a zoologist, it seems thatin many instances the species used has not been recorded .In still more instances it has been taken on faith to be asstated by biological supply houses, which have beenquick to appreciate a demand, but apparently rathermore tardy in building up the expertise necessary to dis-criminate between the members of a range of animals ;even the editors of the present volume are occasionallyliable to refer to 'the planarian'.

So what does it all amount to? Where have we got sofar and where do we go from here? We must, I think,accept that the behaviour of planarians can be predict-ably altered by manipulating their individual experience .One can waste a lot of everybody's time arguing whetherthese changes are correctly labelled learning or sensitiz-ation . The important fact remains that charges of somesort can be produced by training in a wide range ofsituations (from light-shock pairings to T maze) and thatmany of these effects last for weeks. Perhaps not verysurprising and certainly not worth all the fuss. What issurprising, and controversial because, on the face of it,it seems to grind against established theories on thenature of memory traces, is that these long-lasting effectscan survive regeneration . Worse, that they seem to betransferable. The behaviour of cannibal flatworms orworms injected with extracts from trained worms alters.And it doesn't matter a hoot whether one labels thechange learning or sensitization, it is an extraordinarything to happen, considering the time scales involved insome of the experiments . In ten years time, maybe,we shall not consider it odd at all, because by then we maybe able to think of a plausible explanation. In the mean-time, and perhaps in the hope of inspiration, one shouldkeep a watchful eye on the evidence .

MARTIN WELLS