3i6 



NATURE 



\Feb. 6, 1890 



never responded to the challenge, I maintain that he has no 

 right in a scientific discussion to reiterate a statement in support 

 of which he has produced no definite observed evidence. He 

 now returns the challenge to me. But it is no affair of mine. 

 I simply take note of the fact that Prof. Lankester pointed out 

 that the Duke's case collapsed unless the challenge was met, 

 and that the Duke acquiesced by silence. 



Just, however, as with the question of acquired characters, the 

 Duke in defect of direct evidence now tries an a /r/t^n argument. 

 He reminds us of the well known principle of embryology, some- 

 times called the recapitulation theory. Darwin states it in this 

 form : the embryo is "a picture, more or less obscured, of the 

 progenitor, either in its adult or larval state, of all the members 

 of the same great class." 



Now, of course, in the development of the individual organism, 

 we have "a series of incipient structures on the rise for actual 

 U'-e, " if by "on the rise " we mean in process of nutritive growth. 

 This is, however, not necessarily true of the recapitulative struc- 

 tures which may or may not be temporarily utilized. When they 

 are not so utilized they are mere survivals, and we know that 

 survivals constantly so completely fall out of use, that by mere 

 inspection it is often difficult to conceive what could have been 

 their original function. I may give a single illustration. In 

 flowering plants the homologue of the spore of the vascular 

 cryptogams is still preserved. Within it, previous to fertiliza- 

 tion, certain rudimentary structures are developed. It has been 

 shown that these are the last recapitulative remnant of an in- 

 dependent series of structures developed outside the spore in the 

 fern. In that type they form the prothallus, which possesses all 

 the attributes of an independent organism, assimilates, respires, 

 often reproduces itself asexually, and finally bears the sexual 

 reproductive organs. All this in the flowering plant is not 

 merely reduced to scarcely intelligible rudiments, but, in ac- 

 cordance with a well-known principle in embryology, it is 

 thrown backwards in the order of development, and never 

 emerges from the spore at all, instead of as in the fern being 

 wholly external to and independent of it. 



In this case we know the recapitulation and the thing reca- 

 pitulated. We infer from their comparison that a fern-like plant 

 was amongst the ancestry of the flowering plant. But I defy 

 anyone, from a mere inspection of what happens in the latter, 

 to form any idea of what happens in the former. From cases 

 such as these it is obvious that the analogy between the deve- 

 lopment of the individual and the evolution of the race only 

 holds for the broad facts of the sequence of stages, and does not 

 give us any information as to the inutility of the structures of the 

 ancestral organisms, or even, indeed, as to the precise period in 

 their life when such structures made their appearance. The 

 Duke's argument may now, I take it, be stated as follows : — 



In the development of the individual organism, incipient 

 organs are useless. 



The development of the individual organism is a recapitulation 

 of the evolution of the race. 



. '. Incipient organs in the evolution of the race are useless. 



I observe that the Duke's estimation of my logical powers is 

 the reverse of flattering. I abstain, therefore, from criticizing 

 this piece of reasoning. For my part I must confess I do not 

 possess an a priori mind . No argument, however ingenious, is 

 as convincing to me as accurately observed facts. If the Duke's 

 convictions are laws of Nature, the objective verification ought 

 to be forthcoming. W. T. Thiselton Dyer. 



Royal Gardens, Kew. 



The Duke of Argyll supports his assertion that "all organs 

 do actually pass through rudimentary stages in which actual use is 

 impossible " by reference to the stages of embryonic growth. 

 Surely the assertion remains merely an empty repetition of the 

 Darwinian position that the development of the embryo sum- 

 marizes the morphological history of the race. 



The modern dress coat has developed from a mere blanket, 

 but even the useless parts of the modern coat can be easily 

 shown to have had their use in some anterior forms of completed 

 coat. The embryo, like the coat, preserves traces of evolutional 

 stages at which what now appear useless characters were in 

 reality actual useful characters. 



What the Duke has to show is some instance of a completed 

 organ in a completed organism, useless to that organism, not 

 phases in the growth of an organ affording a blurred copy of 

 some form of the organ existent at an anterior stage of the 

 organism, and then useful to it. So far he has merely 



confounded ontogenal steps of growth with phylogenal phases 

 of plan. F. V, Dickins. 



Burlington Gardens, February 3. 



Eight Rainbows seen at the Same Time. 



The following letter which I have just received from Dr. 

 Percival Frost of Cambridge, may interest your readers. 



The theory of the rainbows produced by the sun itself directly, 

 and by the image of the sun reflected from still water, is given 

 in Prof Tait's book on "Light." The phenomenon seems to 

 have been observed by Halley in 1698 (see Nature, vol. x. 

 pp. 437, 460, and 483 for interesting correspondence on the 

 subject). 



The diffuse rainbow produced by the image of the sun re- 

 flected from a white cloud after sunset, described by Mr. 

 Scouller, is, I believe, a novelty. 



William Thomson. 



The University, Glasgow, January 31. 



In Nature (January 23, p. 27i)yougivealetter from Mr. Scouller 

 describing an interesting case of a rainbow, due to the image of the 

 sun in water, which, with the ordinary primary and secondary 

 bows, make up (there being no secondary to that formed by 

 the reflected sun) the three which he saw. Here is a short 

 account of what I saw long ago, almost in prehistoric times, in 

 Scotland, where such sights ought, according to your corre- 

 spondent, to be very commonly seen. I may mention that I 

 saw at the same time, lasting some five minutes, eight well- 

 defined rainbows of one sort or another. 



In 1841, during the time of a long vacation party, spent 

 at Oban, I walked out with my brother to Dunstaffiiage, 

 and we were on the top of the Castle, somewhere between 

 3 and 4 p.m., on a day in the middle of August. Not 

 a breath of wind, bright sun over, I think, Lismore 

 Lighthouse, dusky clouds all over Ben Cruachan and Conoll 

 Ferry ; the sea in the bay (bounded by Dunstaff"nage in 

 the west) as smooth as a pond. Gradually there appeared 

 before us the astonishing sight of the aforesaid eight distinct 

 rainbows, viz. primary and secondary ordinary bows ; pri- 

 mary and secondary bows by reflected sun ; primary tanci 



