March 9, 1S93J 



NATURE 



439 



considerable rocking and using boats of more advantageous 

 forms than mine, if it will be possible to have a much higher 

 speed than 2000 metres per hour. It appears also that the 

 available force will be hardly sufficient to struggle successfully 

 against strong winds and currents. 



I do not therefore prognosticate too confidently any practical 

 value to the motor, but should be very glad if some of your 

 readers would inform me as to any similar experiments which 

 may already have been made. H. Linden. 



Zoological Station, Naples, February 19. 



Blind Animals in Caves. 



As a reader of Mr. Herbert Spencer's writings and a disciple 

 of his, I shall be very glad to lift Prof. Lankester's glove. In 

 the first place I would point out that the process he describes is 

 not natural selection in the ordinary sense ; natural selection is 

 the death of the unfit and the survival of the fittest. In the 

 suggested process neither the animals with perfect eyes, nor those 

 with imperfect, are destroyed in the struggle for existence ; they 

 are simply segregated. But this is of minor importance. The 

 question is whether there is any foundation for the hypothesis 

 suggested. 



Prof. Lankester supposes that the individuals born with defec- 

 tive eyes have remained in the dark places, while those with 

 perfect eyes have followed the glimmer of light and escaped. 

 But he has overlooked the fact that blind cave-animals 

 are horn or hatched at the present day zvith well-developed 

 ■eyes. It is clear, therefore, as in every other case to which 

 the law of recapitulation applies, that the variations 

 to which the evolution is due occurred at a comparatively late 

 period in the life of the individual. Why did not all the indi- 

 viduals escape when they were young, and could still see with- 

 out spectacles? When the imperfection of the eyes did occur, 

 what ground is there for assuming that it was a congenital 

 variation ? It seems to me perfectly certain that it was a 

 deterioration of the eyes caused by the fact that the individual 

 had lived in the dark all its life. In short, I hold that the law 

 of recapitulation in development, the law of metamorphosis, or 

 biogenetic law, as Haeckel called it, is itself a sufficient proof of 

 the inheritance of acquired characters. This argument has never 

 been met or even considered by any of those who talk of con- 

 genital fortuitous variations without defining them. 



The evidence for the statement I have made is, I confess, not 

 <}uite complete, but it is sufficient for my present purpose. In 

 Semper's "Animal Life," p. 80, there is an account of Pin- 

 notheres Holothuruc, based on the author's direct observations. 

 This species lives in the respiratory trees of Holothurians, and 

 in the adult the eyes are degenerate and invisible on the exterior 

 of the animal. The young is hatched as a zoasa with perfect 

 typical eyes ; even when it enters the host it retains its eyes, but 

 afterwards the eyes degenerate and become covered over by the 

 carapace. In the common mole, to take an instance among 

 mammals, the optic nerves are degenerate in the adult, so that 

 there is no connection between eye and l:>rain ; but in the 

 embryo both eyes are connected with the brain by well-developed 

 optic nerves. I am not at present acquainted with any obser- 

 vations on the young of Proteus, or the blind fish Amblyopsis, 

 or the blind Crayfish of the mammoth cave, but I am quite con- 

 fident that the young in all these cases have relatively well- 

 developed eyes. At any rate Prof. Lankester to support his theory 

 must prove that they are blind from the beginning ; for if they are 

 not then it is clear that the variations which we have to consider 

 took place during the life of the individual living in the dark, and 

 consequently the support of Prof Lankester's suggestion vanishes. 

 Prof. Lankester again writes of the deep sea as though it were 

 as destitute of light as the mammoth cave, or the subterranean 

 home of the Proteus, but this is notoriously not the case. With 

 regard to fishes, Dr. Giinther says that below the depth of 200 

 fathoms small-eyed fishes as well as large-eyed occur, the 

 former having their want of vision compensated for by tentacular 

 organs of touch, whilst the latter have no such accessory organs, 

 and evidently see only by the aid of phosphorescence ; in the 

 greatest depths blind fishes occur with rudimentary eyes, and 

 without special organs of touch. Dr. Giinther mentions fifty- 

 one species of fishes living at depths beyond 1000 fathoms, and 

 among these on\y ihree Afihyonus ^elatinosus, Typhlonus nasus, 

 and Ipnops Mttrrayi are blind. It is, I think, sufficiently evident 

 that the biology of the deep sea is quite different from that of 

 subterranean caves or habitats. J. T. Cunningham. 



Plymouth, February 27. 



NO. 12 19, VOL. 47] 



Besides panmixia and emigration of the more perfect-eyed 

 individuals, as explained by Prof. E. Ray Lankester, allow me 

 to suggest another cause for the dwindling of the eyes in cave- 

 dwelling animals. 



Prof. Weismann says that the degeneration "can hardly be of 

 direct advantage to the animals, for they could live quite as well 

 in the dark with well-developed eyes." I submit, however, that 

 in a place permanently dark the eye is not merely useless, but, 

 as a delicate and vulnerable part, it becomes a positive source 

 of danger to the animal. No longer helping the creature to 

 avoid obstacles or danger, it is, in proporti( n to its size, exposed 

 to injury, destructive inflammation, and the attacks of parasites 

 in a manner which must not seldom lead to the death of the 

 individual. As other senses become more acute, and the eye 

 recedes, this danger diminishes, and when the eye has become 

 a mere rudiment, " hidden under the skin," its presence ceases 

 to be a disadvantage, and so degeneration does not proceed to 

 complete suppression. 



It is a wonder that Mr. H. Spencer should have overlooked 

 Prof Lankester's explanation, for the English editor of Prof 

 Weismann's fifth essay has not failed to call attention to it, 



Mirfield, February 27. A. Anderson. 



[Daiwin has himself drawn attention, in regard to burrowing 

 animals, to the conditions pointed out in the above (" Origin of 

 Species," 6ih edition, p. no). — Ed.] 



Foraminifer or Sponge ? 



I AM glad to find that Mr. Pearcey agrees with me in regard- 

 ing Neusina Agassizi, Goes, as identical with Stamiophyllum 

 zonarium, Hasckel. But with respect to its systematic position 

 I do not as yet see sufficient reason to differ from Prof Haeckel 

 in regarding it as a sponge, although I have never observed 

 flagellated chambers and cells any more than he. The large 

 masses of foreign bodies always present in this organism offer 

 very serious difficulties in seclionising it, and as long as we are 

 not absolutely certain about its cellular structure we are justi- 

 fied in thinking with Haeckel that general appearance and the 

 presence of oscula, pores, subdermal cavities, horny skeleton, 

 &c., are sufficient to characterise the form as a sponge. 



Mr. Pearcey mentions six genera of Foraminifera which he 

 thinks approach closely to Stannophyllum, I am sorry I cannot 

 see much similarity. The chitinous lining in the tube-like body 

 of some Foraminifera certainly bears not the slightest resem- 

 blance to the distinct fibrous stroma of Stannophyllum, which 

 reminds me much more of the filaments of the true horny sponge 

 Hircinia. If anything tells in favour of Mr. Pearcey's view, it 

 is the concentric lines of Stannophyllum, which recall the fora- 

 miniferal rather than the sponge type of growth. 



The final decision of this question can of course only be 

 expected from an examination of the cell structure. 



University College, Liverpool, R. Hanitsch. 



February 25. 



A Magnetic Screen. 



During the last vacation St. John's College, Oxford, has 

 been lit with the electric light, and a transformer of the dyna- 

 momotor type, weighing over seven tons, has been placed within 

 about sixty feet of the electrical testing room of the Millard 

 Laboratory, which is furnished with several reflecting galvano- 

 meters. I greatly feared that the instruments would suffer much 

 from the magnetic field of the large transformer. When it was 

 found that no other space could be given up for the machine, 

 I devised a method of construction which the Oxford Electric 

 Lighting Company very kindly carried out for me when build- 

 ing their dynamo house. My method is to construct a wall of 

 scrap iron round the three sides of the dynamo nearest to our 

 laboratory. The iron wall is about eight inches thick, and is made 

 by building two brick walls parallel to one another, and filling 

 the interspace with scrap-iron ; a delicate magnetometer used 

 for testing the field at unprotected and protected points equi- 

 distant from the magnets, when the machine is in action and not 

 so. shows that the iron wall is an effective barrier to the magnetic 

 influence. I venture to make known this method of shielding 

 off a magnetic field, because in these days of electrical invasion 

 it may be of use in protecting physical instruments from being 

 seriously disturbed, and rendered useless for any but the 

 roughest determinations. Frederick J. Smith. 



Trinity College, February 28. 



