DISCOVERY 



Living Backwards 



By J. S. Huxley, M.A. 



l-'cllow o/ A'fii' Collcyc, Oilunl 



One of the great scientists of last century declared 

 that Science was organised common sense. In a way 

 it is ; but in another way, how emphatically it is not ! 

 Perhaps we might say that it is a continual upsetting 

 of the judgments and most firmly-held doctrines of 

 common sense by an extension of common sense's 

 own methods. 



The motion of the earth round the sun, the muta- 

 bility of species, the possibility of interchanging all 

 the different forms of energy, the production of water 

 by burning h\-drogen in oxj'gen — how unlikely are all 

 these facts, how much opposed to the common-sense 

 ideas of common-sense people, but how undeniably 

 true ! 



Common sense is content to generaUse broadly and 

 vaguely from just so much experience as necessity 

 thrusts under its nose ; science is for ever searching 

 for more experience, which it may compare with 

 what it already possesses. In its method of dealing 

 with facts, science is but organised common sense ; 

 but in its method of collecting facts, it is common 

 sense no longer. Common sense is content with 

 every-day ; but science is organised curiosity. 



This part-antithesis between science and common 

 sense is to-day being once more exemplified in relation 

 to some of the most fundamental processes of life. 

 To common sense it would seem obvious that develop- 

 ment is a closed C3'cle, each stage leading forward in 

 an inevitable series to the next. The fertilised germ 

 becomes the embryo, the embryo becomes the young 

 or ganism ; youth leads to maturity, maturity to age, 

 and age to death. That is the normal cycle in man 

 and in the animals and plants with which common 

 sense is familiar ; it knows no facts that contradict 

 the notion, and so the notion becomes a generalisation. 



But science is not content with the familiar. An 

 organism is an organism, whether it be a jelly-fish, a 

 snail, or a dog ; and all organisms are related. In 

 some organisms the processes of development are not 

 necessarily irreversible ; and we are approaching the 

 time when we shall be compelled to assert that these 

 processes are fundamentally reversible, and that the 

 irreversibility of our own life-history is only secondary. 



Among marine animals there exists a curious group, 

 the Tunicates, for long classified with the sholl-fish 

 until a study of their embryology revealed that they 

 passed through a tadpole-like form, and that they 

 were, in fact, poor relations of the Vertebrates, fixed 

 by the head, having lost their eyes and ears, and 



feeding on mn loMopic jiartules brought m by a 

 ciliary current. One of them, ClavtUina by name, 

 was found by Driesch to possess the extraordinary 

 faculty of returning to a simpler condition. The 

 adult animal, pellucid, revealing to the microscope 

 every detail of its elaborate anatomy — gill-slits, food- 

 groove, stomach and intestine, liver, heart, minute 

 brain — can, when damaged or placed in unfavourable 

 conditions, altogether change its aspect. Its inhalant 

 and exhalant orifices close, it gradually becomes 

 opaque as it shrinks, and its various organs grow 

 simpler and simpler, the cells of which they are com- 

 posed losing their characteristic form, and becoming 

 all approximately cubical. Finally, in the course of 

 a week or two, the creature has become nothing 

 more than an opaque white ball, covered with a 

 single layer of epithelium ; the internal organs are 

 reduced to a few closed vesicles, and the space between 

 them and the skin is packed tight with the blood- 

 corpuscles. If now replaced in pure sea-water, it 

 will retrace its upw-ard development and become a 

 normal individual again, perfect, but smaller, since a 

 certain amount of material has been used up in the 

 metamorphoses. The animal has been e.xperimentally 

 made to repeat this reversal and subsequent blossom- 

 ing-out three times ; and if it could be supplied with 

 enough food to bring it up to its original size (unfor- 

 tunately it is difficult to feed in the laboratory), it 

 could no doubt continue to do so indefinitelj'. Such 

 a process, which we may style dedifferentiation fol- 

 lowed by redifferentiation, is clear evidence of the 

 possibility of reversing development. 



A different type of reversal is seen in many common 

 flat-worms and sea-anemones. The Planarian flat- 

 worms are among the simplest forms of three-layered 

 animals. None the less, they have a sufficiently 

 complex organisation, with brain-ganglion and nerve- 

 cords, prehensile proboscis, branched digestive and 

 excretory systems, simple ej-es, and very elaborate 

 reproductive organs. The sea-anemones are, of course, 

 highly organised polyps — two-layered creatures, with 

 radial symmetry, a circle of tentacles and a central 

 cavity divided up by a number of strengthening 

 partitions. 



If one of these animals is starved, it does not die 

 after losing a quite small amount of weight, as does 

 a man, but gets smaller and smaller, saving itself from 

 death by feeding upon itself. Sea-anemones several 

 inches long have been made to shrink until they were 

 no longer visible to the naked eye. 



It is, however, the flat-worms which have been most 

 thoroughly investigated. Some years ago, it was 

 pointed out that a flat-worm which has been much 

 reduced in size by starvation comes to resemble 

 similar-sized young individuals of the species in all 



