486 



NATURE 



[March 23, 1893 



Glaciers have, however, without doubt caused lakes in cases 

 where they have dammed up the mouth of glens with detrital 

 matter. The enormous masses of such matter which dam up 

 the waters of the northern Italian lakes are most impressive. 

 But it does not follow that the glaciers which left those great 

 masses also scooped out the deep bed and rocky walls of the 

 Lake of Como. 



My own belief is that the great recency of large earth move- 

 ments is one of the facts of geological science which has yet to 

 be accepted ; and that the slowness with which it has made 

 progress, or has even .been overborne, is entirely due to 

 very natural preconceptions and general assumptions about 

 the stability of the earth surfaces, such as those which 

 find expression in Mr. Wallace's very interesting and significant 

 paper. Argyll. 



Inveraray, Argyllshire, March il. 



P.S. — Recent calculations in America seem to bring down the 

 possible date of the close of the glacial epoch there to little 

 more than lo.ooo years. 



The Cause of the Sexual Differences of Colour in 

 Eclectus. 



Mr. F. E. Beddard says in his suggestive work on " Ani- 

 mal Coloration" (1892, p. 3) :— 



" Sometimes differently coloured animals have in reality the 

 same skin pigments. The attention of the reader will be directed 

 in a later chapter to the remarkable difference in colour be- 

 tween the males and females of certain parrots. In Eclectus 

 polychlorus this sexual dimorphism is extremely marked. It 

 would be an exceedingly anomalous fact if the same species of 

 bird were to possess different pigments in the two sexes ; and as 

 a matter of fact it is not so in this parrot, different in colour 

 though the two sexes are. The same pigments are present, but 

 the structure of the feathers is different, and thus the resulting 

 colour as seen by the eye is different." 



The last sentence (the italics are mine) is not consistent with 

 late Dr. Krukenberg's investigations on the colours of feathers. 

 The case is not one of structural difference in the feathers, for 

 Ihe differences in colour between male and female of Eclectus 

 are occasioned by the presence or absence of the pigment itself. 

 The green colour of the male results from a yellow pigment 

 {psittacofulvin) lying over a blackish brown one {fuscin), but 

 the blue colour of the female (^. linnei, auct.) simply results 

 from the absence of the yellow pigment. The dark pigment 

 {fuscin) is present and the incident rays of light are reflected 

 from it, passing through a zone without pigment, which zone 

 absorbs the rays of the red extremity of the spectrum. Here 

 the same conditions occur which effect the blue colour of the sky. 

 The blue is an optical colour, as is the green, but a different 

 structure of the feathers does not come into question. The red 

 colour both in male and female is effected by a red pigment, 

 which is the same in both sexes, the differences in shade (as 

 also the violet in E. grandis, e.g.) depend on the quantity of this 

 colouring substance and in the absence or presence in different 

 quantities of the underlying /?«a«. The pigment of the yellow 

 feathers in the female of ^. grandis is the same as the yellow pig- 

 ment in the green males. Dr. Krukenberg supposes that these 

 different pigments are derived from one and the same ground 

 substance, a supposition which appears to be very plausible. 



Why the yeHow pigment of the male is not developed in the 

 blue parts of the female we do not know, nor why the different 

 pigments in Eclectus are disposed just as they are, since we are 

 in general quite ignorant about the causes of the disposition of 

 colours in bird feathers ; but in the case under discussion a 

 "different structure" of the feathers would not give as sufficient 

 an explanation of the facts as does the above. Touching the 

 causa movens of the different colours in the sexes of Eclectus, we 

 can only say that it is sexuality, but this, of course, is no mechan- 

 ical explanation, i.e. no true explanation at all. We can only 

 say that in most birds the male offers an overplus of colour as 

 compared with the female, which overplus no doubt has a relation 

 to the more vigorous biological processes or superabundant 

 vitality in the male during certain periods, and this also holds 

 good in Eclectus, as we see that the female wants the yellow pig- 

 ment which the male possesses. But we must bear in mind 

 that in Eclectus. the young ones from the egg display already 

 these sexual differences of colour, a fact which is as remarkable 

 as it is rare. 



NO. I 22 I. VOL. 47I 



For reference see C. Fr. W, Krukenberg, "Die Farbstoffe 

 derFedern," four papers in Vergl. phys. Studien, 1881 sq., and 

 my papers, Mitth. orn. Ver. Vienna, 188 1, p. 83, ncc^ASitz.ber. 

 Akad. IViss. Berlin, 1882, p. 517 sq. 



Dresden, March 8. A. B. Meyer. 



Blind Animals in Caves. 



Mr. Cunningham's notion as to what constitutes "a fact" 

 would appear from his letter published in your issue of March 9 

 to be peculiar. It is of course only through inadvertence 

 that he declares a mere supposition to be a fact, and states that 

 I have " overlooked " it. His words are "he (Prof. Lankester) 

 has overlooked the fact that blind cave-animals are born or 

 hatched at the present day with well developed eyes." Further 

 on he proceeds to state that no such fact is known or recorded, 

 but that he is "quite confident" that the young of blind cave- 

 animals have well developed eyes. 



I am quite aware that an important test of the truth of my 

 theory of the origin of blind cave-animals would be found in the 

 details of their embryonic development, but cannot think that 

 Mr. Cunningham is justified either in his confidence as to the 

 result of a hitherto unattempted embryological research or in 

 asserting what is at variance with his own subsequent avowal, 

 viz. that there are facts ascertained as to the condition in which 

 blind cave-animals are born, which I have ignored. 



E. Ray Lankester. 



Lunar "Volcanoes" and Lava Lakes. 



I HAVE waited some time to see what replies might be made 

 to Mr. J. B. Hannay's suggestion, that lunar walled plains may 

 have been due to tides in the molten nucleus during crust 

 formation (Nature, vol. xlvii. p. 7). 



There seem to be at least two objections to the " volcanic " 

 theory of lunar surfacing. First, that there must have been 

 during the earlier, and indeed later, stages of it a vast gaseous 

 and vaporous envelope, which, as secular temperature slowly 

 declined, would be condensed to form seas, giving rise to a long 

 era of erosion, and extensive denudation, and formation of sedi- 

 mentary strata, as on our earth. There are no traces of this on 

 our moon, the surfacing of which is conspicuously destitute of 

 evidences of drainage phenomena. Secondly, there is an entire 

 absence of distinct local colour in the detail, which should be 

 easily seen in volcanic deposits unencumbered by vegetation and 

 weathering. , 



I leave it to geologists and physicists to say if they thmk it 

 at all likely or possible for any globe like our moon to pass 

 from the semi-incandescent, lava-crusted stage, with huge 

 vaporous envelope, to the cold, airless, and waterless condition 

 of our satellite without passing through a very prolonged era 

 of erosion, which, as in our case, would obliterate all traces of 

 the former era. 



Judging by our vast series of stratified rocks, we are led to 

 conclude that an exceedingly long temperate era oferoSionmust, 

 in the very nature of things, supervene on the heated lava 

 stage in all planetary development, quite obliterating the 

 relics of the volcanic era and relaying a sedimentary surfacing. 



Taking up the second objection, in re the marked absence of 

 colour, I would point out the abnormal brightness, or even 

 brilliancy,of the lunar cliffs and steep inclines all over the surface. 

 It is precisely at such places that astronomers expect to see the 

 nature of the surface and degradation due to the effect of gravi- 

 tation, i.e. where (exposed to unmitigated solar heat in the day, 

 and a cold probably below - 100° C. at night) the cliff-falls would 

 be most frequent, and the true colour of the strata most visible. 



Proctor in his "Moon " (pp, 301-2) says : — " In each lunation 

 the moon's surface undergoes changes of temperature which 

 should suffice to disintegrate large portions of her surface, and, 

 with time, to crumble her loftiest mountains into shapeless heaps. 

 In the long lunar night of fourteen days a cold far exceeding 

 the intensest ever produced in terrestrial experiments must exist 

 over the whole unilluminated hemisphere." 



Neison, on page 113 of his "Moon," also says: — "That 

 physical changes of various characters must be still occurring 

 upon the moon is rendered certain by . . . the alternate heating 

 and cooling of the lunar strata ; from the nature of the expansion 

 and contraction thus brought into play must, through numerous 

 fractures of the resulting general disintegration, gradually ruin 

 all the lunar formations." Thus " considerable changes must 



