188 
plement had been finished. The general views on Protoplasm 
are given under Ce//s, Ameba, and so far as it is identical with 
Sarcode under Actinophrys, Sarcode, and other headings in E.C.S. 
Rhizocrinus is referred to under London Clay, and its occurrence 
in the living state mentioned. Aerolites: The latest reference is 
said to be 1861, implying, as it seems, that none of the informa- 
tion is of later date. Falls subsequent to 1861 are mentioned, 
and many of the facts are of later date ; as, for example, those 
relating to the Alais and Orgeuil aerolites ; Sorby’s conclu- 
sions published in 1865 ; and Daubrée’s experiments, of which 
accounts were given in 1866 and 1868. The article itself 
appeared early in 1869. As to the bibliography, the principal 
authors are mentioned, and a list of the works consulted was 
written, but was inadvertently omitted. It is also said that the 
latest reference under A/ca is 1861, but this again is not correct. 
The writer of the article Anvelida was not aware of Claparéde’s 
strictures at the time he wrote it ; but, after all, they do not seem 
to affect materially the general statements given in the supple- 
mentary volume. Prof. Huxley’s views respecting the systematic 
position of Archeopteryx are given under Birds, E.C.S. No 
reference is made to Profagon under Blood, E.C.S., nor is men- 
tion made of Day’s colour tests, nor Dr. Richardson's renuncia- 
tion. Of the last, all that was found in the Reports of the 
British Association is the title of his paper, which runs 
thus, ‘On Coagulation of the Blood; a correction of the 
Ammonia theory,” and of which nothing more is said. 
Hence it was thought best to say nothing about the matter. Of 
the long string of terms which ‘‘ Nemo” has culled from Prof. 
Hurxley’s last address to the Geological Society, and which are 
said to be omitted, the majority are given in the Supplement. 
For instance, to cite one or two cases: Anthracosaurus occurs 
under Carboniferous system, E.C.S. ; Evolution under Paleon- 
tology; Micrelestes under Rhetic Beds; and so on. As to the 
other remarks which have not been specially alluded to, it may 
be admitted that some of the articles might have been improved. 
Foraminifera would have been all the better if Haeckel’s 
volume had been consulted, only Haeckel’s work could not be 
got. It would have been very desirable if subjects which 
have been omitted had been inserted, and if cross references 
had been more numerous; but there were restrictions as to 
space which rendered it necessary to make a selection. Thus, 
Meloe was inserted and Sphegide rejected, because there was no 
room for both. What a Cyclopzedia ought or ought not to con- 
tain is an open question. It cannot give information upon 
everything; and probably very few persons not specially in- 
terested in the subject want to know about //yenictis or 
Ictitherium. Uf regard was had to the theoretical view of the 
matter, and not to the cost and other practical drawbacks, a 
full account of all that has been done in the last sixteen years 
would fill several volumes as large as the Supplement to the 
“ Natural History Division of the English Cyclopedia.” I beg to 
sign myself 
THE EDITOR 
Cuckows’ Eggs 
Wuar is the drift of this discussion on the eggs of the 
cuckow? Is it ‘‘natural selection,” “mimetic analogy,” or 
what? Are we to understand that by some process of ‘natural 
selection” the European cuckow can change the appearance of 
her egg to that of the selected foster parent? or that one set of 
cuckows lays eggs like titlarks, let us say, another like hedge- 
sparrows, and so on; and always select each its particular nest 
in which to deposit its particular coloured egg? 
If this is it, cz dono ? Of course to deceive the foster parent. 
Is this needed? Idoubtit. Ido not think the foster parent 
cares what coloured eggs she sits on, so long as they are about 
the size of her own, so as not to inconvenience her. 
Let us see what cuckows do in other countries, and let me 
select Africa as my field. If deception is necessary in one 
country, why not in another? Le Vaillant is so inaccurate 
that one must take all his statements cum grano, but he is 
right in some things, where, I suppose, he had no temptation 
to go wrong. He says of Cuculus gularis ‘‘that its egg is 
olive grey, dotted with red” (gris olivacé, piqueté de rouge), 
and that it is laid -in the nests of—1, the Jean Frédérick 
(Bessonornis phenicurus) ; 2, Corypheé (Bradyplerus coripheus) ; 
3, Traquet-patre (Pratincola pastor) ; 4, Pie-griéche fiscal 
(Lanias collaris); and 5, Bacbakiri (Zelophonus bacbakiri). 
Now the eggs of No, 1 are of a dirty white or buff ground, 
NATURE 
[Huly 7, 1870 
more or less spotted with pale rufous; 2, a lovely verditer, 
irregularly blotched with brown; 3, also verditer, idistinctly 
clouded with brown; 4, pale grey, blotched at the obtuse end 
with greenish and reddish spots ; 5, light blue, profusely spotted 
with brown. 
Cuculus solitarius, he says, lays its pink egg, dotted with 
clear brown spots, in the nests of—1, Bessonornis phenicurus ; 
2, Bradyplerus coriphaus ; 3, Le Capocier (Drymoica capensis) ; 
4, Le Reclameur (Zessonornis vociferans); and 5, Le fauvette 
a téte rousse. The eggs of the last two I do not know; 
those of the first two are described above ; those of No. 3 are 
blue, with brown blotches. 
Oxylophus edolius and O. melanoleucus he confounds to- 
gether, but it matters little, as the eggs are alike—pure white— 
and deposited in nests of—1, Bergeronette brun (A/ofacilla 
capensis) ; 2, B. corypheus ; 3, Gobemouche mantelé ( 7chitrea 
cyanomelas) ; and others, whose eggs I do not know. Of 1, 
the eggs are greyish white, or rather nankin, minutely freckled 
with brown ; of 3, they are cream-coloured, profusely spotted 
with red, brown, and purple spots, in a band at the obtuse end. 
One of my correspondents finds eggs of O. edolius in the 
nests of Pycnonotus capensis, whose eggs are rather deep lake, 
profusely spotted with dark markings! They also, I know, lay 
in the nests of Pycuonotus nigricans—eggs as of the last. I 
found Mud-birds (Aalacircus bengalensis) in Ceylon, feeding a 
young O. melanolewcos, and their eggs are of a uniform deep 
verditer. 
Chalcites auratus lays white eggs also, and some of my corre- 
spondents have sent what I Jdelzeve to be their eggs taken from 
the nests of Hyphantornis capitalis, whose eggs are green, pro- 
fusely speckled with brown, and dark salmon-colour profusely 
speckled and spotted with dark brown and black. 
Now, will any one say, after comparing these different cuckows’ 
eggs with those of the nests in which they have been found, that 
there is any attempt at imitation, and if not in so many cases, 
why in that of C. canorus ? 
I used to think and so I wrote (‘‘ Birds of South Africa,” 
p. 252) that the eggs of parasitic birds ‘‘ usually resembled those 
of the foster parent.” This was my idea founded on statements 
concerning the European cuckow taken from books; but a valued 
correspondent, taking exception to my position, set me to inves- 
tigate the subject for myself, and to collect together and analyse 
my own observations and those of my collectors in this country. 
She writes as follows :—‘‘ The eggs of all the cuckows that I have 
met with in this country (South Africa) are white, and moreover 
they are nearly always larger than the eggs of the bird in whose 
nest they are deposited. With regard to distinguishing eggs, 
birds of all kinds are exceedingly short-sighted. We used to 
amuse ourselves by changing the eggs in all the birds’ nests we 
knew of. The owners seldom left them, but took to the strange 
eggs; and unless their habits were remarkably different, they 
would blindly rear each other’s young, just as they do the young 
cuckows. It is not necessary, therefore, for nature to make this 
provision. My second son once filled a Cape canary’s nest with 
so many eggs that when the young were hatched they were 
more than the poor birds could manage to provide for, and 
having repented of his mischief, he was obliged to help them 
bring up their young.” (Cf. Zdis, 1868, p. 247.) 
Since this was written, I have had the advantage of visiting 
my correspondent, who is well known throughout this colony 
for her talents, love of natural history, and powers of obser- 
vation. We often discussed this subject. She and her sons 
assured me they never cared to select eggs like those of the 
foster-parent, but simply eggs of those whose food they knew 
to be similar. They said the confusion they caused was most 
amusing, but only after the young were hatched. The eggs 
were incubated without any demur on the part of the foster- 
mother. After this, surely I may ask cui bono the C. canerus 
imitation ? E. L. LAyARD 
Cape Town, Cape of Good Hope, May 3 
The Chromatic Octave 
I HAVE to thank ‘* M. A.” for his letter in NATURE of June 
oth, suggesting that the wave-frequency to which the comple- 
mentary of any tint is due, may be, not the geometric mean 
between that tint and its octave, as I suggested ina letter in 
Nature of 28th April, but the harmonic mean. I can scarcely 
doubt that there must be some simple arithmetical relation 
between the wave frequencies of any tint and its complementary, 
