August 1, 1895.] 



KNOWLEDGE. 



183 



Jlira 



statement, and he replied, February 20th, saying, 

 has just had two maxima." 

 My record continued reads : — 



March 2nd .. 0'2 S, y 7-0 

 March 5th ... 0-4 i5, y 80 

 March 8th ... 0-4 8, y 7-0 

 March 12th ... Moonhght and cirrus. 

 March 16th ... 0-3 I. 

 From these figures it appears that there were other 

 changes in light, and on March 20th the same astronomer 

 wrote me, " Mira fluctuated greatly. My last observation, 

 March 14tb, 4-32. It then became impossible to observe 

 it in consequence of the companion stars being too near the 

 horizon for accuracy at such a distance, &c." Please notice 

 the photometric estimate, 4-32, and my visual estimates, 

 March 8th and IGth ; — o is 4-2 magnitude. There was no 

 apparent change in Mira from March l(ith to 20th, when it 

 had fallen too low in the city smoke and vapour for safe 

 comparison with stars so far above it. 



Herr Plassmann's maximum reminds me of a note in 

 Nature, March 8th, 1894, p. 442, which says that, "although 

 the maximum of Jlira was predicted for February 17th, 

 yet on March 4th it was only a trifle brighter than J, a 

 star of 4-2 magnitude." The maxima of li-i94 and 1805 

 are in accord and doubtless follow Argelauder, but Herr 

 Plassmann's maximum indicates a correction of thirty days, 

 not generally known, or at least accepted. There is a 

 comcidence, however, between his date and this year's 

 observations here. 



Col. Markwick has treated the matter broadly and 

 comprehensively, and I am highly gratified to be in agree- 

 ment with so distinguished an authority. I beg to call 

 his attention, however, to a statement in Webb's "Celestial 

 Objects," volume XL, that Mira is not always ruddy. If 

 there was a tinge of red in it this year it escaped my 

 notice. 



I\Ir. Peek holds, I submit, an extreme view on visual ob- 

 servations, and the record above afl'ords some little evidence 

 that a fair degree of accuracy may be reached. Of course 

 it requires pains, a good eye, and steady atmosphere. 

 Some excellent work of this kind has been done in this 

 country. There is a triplet of variable star observers 

 in Massachusetts, ^lessrs. Chandler, Yendell, and Sawyer. 

 The last-named works with a field glass, while the others 

 have all the modern appliances, and they wait a long time 

 for his concurrence before making an announcement, thus 

 showing a high appreciation of visual observations. 

 Their work is well known. 



In conclusion I would say that my observations have 

 been recorded nightly, according to my best judgment, 

 and without any reference to any previous entries. 



I enclose the notes of the astronomer alluded to for 

 your inspection. 



Yours truly, 

 Memphis, Tenn., David Fl.^nery 



12th -June, 1895. 



COLOURS OF BUTTERFLIES. 

 To the Editor of Knowledge, 



Sm, — In your July number, Mr. MUler, in criticizing 

 Dr. Marshall's paper upon this subject (ante, p. 128), draws 

 from it a number of conclusions that he says are " plainly 

 deducible," but at which I am at a loss to see how he 

 can arrive. 



Mr. Miller asks why some insects are protected and 

 others are not, and why the latter have survived if 

 protective colouring is a necessary clause. 



In answer I would point out that the fact that many 

 forms do exist without the aid of special protection, is 

 conclusive proof that in such cases special protection is 

 unnecessary. This is obviously a truism. 



Special adaptability to an environment is the direct 

 result of high competition, and the higher this competition, 

 the fiercer this struggle between the offensive and defensive 

 forces at work, the sooner, on either side, will approximate 

 perfection be attained. 



This perfection is reached, not merely by the production 

 of strong forms, but by the weeding out of the weak ones, 

 and as such a process necessarily entails an extra expendi- 

 ture of energy in the reproductive system, the tendency 

 would be for every organism to remain in as imperfect a 

 condition as its environment would permit. 



Hence, to me, it would appear to be the rule that 

 a special amount of protective form or colouring is 

 exhibited only where an exceptional opposition from 

 numerous or powerful enemies has to be met ; and, 

 inversely, that where an organism shows no close sym- 

 pathy with its surroundings, the struggle for existence is 

 not severe. 



Mr. Miller asks why do not all butterflies follow the 

 clever example of their mimicking fellows '? He is looking 

 at the subject quite from the wrong side. The active 

 agent, natural selection, which adapts an organism to its 

 position, is not an internal, but an external force. It is 

 the environment alone which sorts out the bad forms from 

 the good, the " goats from the sheep," and by destroying the 

 former, allows only the latter to inter-breed. Unless the 

 enemies of an insect are numerous enough, or powerful 

 enough, to weed out its weaker forms, that insect can 

 never, except by mere chance, advance one step towards 

 perfection. 



Mr. Miller points out that insects using warning colours 

 " are so considerate as to protect even their enemies from 

 injury." This may be so, but it is only from egoistical 

 motives, and therefore has no serious bearing upon the 

 matter. In the myriad dovetailiugs between the economy 

 of one animal or plant and another, it would indeed be 

 strange if some coincidences of mutual aid did not arise. 

 But can Mr. Miller quote a single instance where any 

 animal or plant behaves in such a way as to benefit 

 another individual or species, to the final injury of itself, 

 or of its type ? That would be a real obstacle to get over. 

 Finally, Mr. Miller raises objection to the word 

 " mimicry," because he says that such a term implies the 

 presence of a degree of inteUigence in the insect world, 

 such as he, very properly, cannot allow of. As I have, 

 however, already pointed out, " mimicry " results from the 

 action of natural selection, and as natural selection is 

 altogether an environmental force, no demand whatever is 

 laid°upou the intelligence of the insect. In favour of this 

 view let me quote a single case. 



When that pretty little moth, Lahophora virctata, first 

 emerges from its pupal skin, it is of a beautifully bright 

 "reen colour, exactly matching in tint the holly trunks 

 upon which it rests. After it has been "out" a few 

 days, this green changes to yellow, and those moths which 

 still maintain their position upon the bark are made con- 

 spicuous objects for any passing enemy. Before that time, 

 however, all the fertilized females have mounted to the 

 higher branches, to lay their eggs among the flowers. 

 Thus only the males and the unfertilized females are left 

 upon the tree trunks, and as both these two are of the 

 least importance in the economy of the type, natural 

 selection has left them alone to the mercy of then- foes. 

 That such yellow forms rest upon the green bark 

 shows that the insects themselves appreciate neither 



