220 
NATURE 
[Fuly 9, 1885 
in the developmental life-history of species. The over- 
whelming amount of evidence which has now been 
obtained of adaptations for cross-fertilisation, not in 
orchids only, but throughout the whole series of flowering 
plants, and the almost constant association of conspicuous 
form, colour, and odour with adaptations for insect fertil- 
isation, force us to the conclusion that in almost all the 
cases adduced by Mr. Forbes we have species which 
were once adapted for insect-fertilisation. But in the 
terrific struggle for existence ever going on in tropical 
regions, insects are subject perhaps more than any other 
group of organisms to excessive fluctuations of numbers, 
sometimes culminating in the complete extermination of 
species ; because they are equally liable to severe injury 
by physical and organic causes—by adverse seasons 
which destroy them in some of their earlier stages, or by 
the excessive attacks of insectivorous animals in both 
their larval and perfect states. It must therefore often 
happen that certain species of insects almost disappear in 
districts where they are usually abundant, and if any 
particular plant has had its flowers so highly specialised 
as to be adapted for fertilisation by one of these insects 
only, it must become extinct unless it occasionally produces 
varieties which are capable of self-fertilisation. The species 
of orchids in which a very small percentage of flowers 
produce seed capsules are evidently those in which the 
special insects adapted to fertilise them have become 
either temporarily or permanently scarce, and if that 
scarcity goes on increasing one of three things: must 
happen—either the flower must become modified so 
as to be fertilised by some more abundant insect, or it 
must become capable of self-fertilisation, or it must 
become extinct. No doubt all these three cases occur, 
but it is of the second alone that we can obtain any know- 
ledge, because we there find, as in our own bee-orchis, 
the special attractions of conspicuous form and colour 
which have yet ceased to be of service to the species. 
But no naturalist can doubt that these attractions were 
once serviceable ; and we are thus led to conclude that 
all such instances are forms of functional degeneration 
which under changed conditions of the environment have 
afforded the only means of preserving the species. 
Mr. Forbes’s record of his thirteen months of travel in 
Sumatra are perhaps the most interesting portions of his 
book. He here met with some of the most marvellous 
productions of the vegetable kingdom—strange parasitical 
Rafflesiacez, an eccentric fig which ran underground and 
there produced its fruit, just showing their tops above the 
surface, and the giant arum (Amorphophallus titanum), 
some of which were seventeen feet high and with tubers 
six feet six inches in circumference. In the same forest 
huge earth-worms raised tubes of mud four and a half 
inches in circumference and eight inches high ; and were 
so numerous as to render the whole surface of the ground 
as rough and hummocky as that of a newly-ploughed 
field. Here too, as well as in Java, he found a wonderful 
case of mimicry in a spider which deceived him even a 
second time ; and he here obtained the rare Ornithoptera 
brookeana, perhaps the most chastely beautiful of all 
butterflies. Grand mountains, active volcanoes, glorious 
forest scenery, strange antique monoliths, and many in- 
teresting races of men, combine to render Sumatra one of 
the finest hunting-grounds yet left for the naturalist, while 
over the greater part of it there are facilities for travel or 
for residence rarely to be found in so little known a 
country. 
In his later and more adventurous explorations of 
Timor Laut and Timor, Mr. Forbes was accompanied by 
his wife, a lady who seems to have endured all the annoy- 
ances, privations, and dangers of such a journey with 
truly heroic fortitude. Although these islands are far 
less known to naturalists than almost any other part of 
the Archipelago, they seem comparatively poor in a 
natural-history point of view. A considerable proportion 
of the birds and butterflies of Timor Laut were new 
species, but the collections were scanty, and there is, no 
doubt, much still to be done there if a collector could 
freely explore the country and not be confined, as was 
Mr. Forbes, to a limited tract owing to tribal warfare. 
One of the interesting discoveries here was another ex- 
ample of mimicry among birds, in which a new species of 
oriole mimics a new honeysucker, just as do correspond- 
ing species in Ceram, Buru, Gilolo, and Timor. A most 
interesting case of protective colouration was also ob- 
served in the white-headed fruit-pigeon of Timor (Pfzlopus 
cinctus). These birds sat motionless during the heat of the 
day in numbers on well-exposed branches, yet Mr. Forbes 
states that it was with the greatest difficulty that either he 
or his sharp-eyed native servant could detect them, even 
in trees where they knew they were sitting. The strongly- 
contrasted white and dark colours of this species are 
such that any person looking at a specimen in a museum 
might take it as an example of a defenceless bird with 
very conspicuous plumage, and might ask triumphantly 
how our theory of protective colouration can be applied 
here. Yet it turns out that these strongly-marked colours 
so exactly harmonise with the colours of the branches of 
the trees on which it sits, exposed to the glare of the 
tropical sun, as to be completely protective ; and we thus 
have another illustration of the impossibility of forming 
any correct judgment on this question unless we are able 
to observe each species in its native country and among 
the exact surroundings to which it has become adapted. 
The hasty journey through the interior of Timor, among 
strange scenery and strange people, is full of interest. 
Most of the mountain tops, where alone a rich and inter- 
esting vegetation was to be found, were strictly taboed, 
and it was often only by stratagem that specimens were 
collected ; while the difficulties of travel in a country 
absolutely without roads and consisting almost wholly of 
an endless series of rugged mountains and deep valleys 
were exceptionally great. 
The book is on the whole very well written, and will 
give the reader an excellent idea of some of the less 
known parts of the Malay Archipelago. The weakest 
part of it are the illustrations, which, though numerous, 
appear to be for the most part reproductions of rough 
sketches by some unsatisfactory process of photo-zinco- 
graphy. For this the author was probably not responsible, 
but his readers will regret that the strange and beautiful 
scenery he has so graphically described is not more 
effectively presented to the eye. The portraits of many 
of the natives are, however, very well done, while several 
good maps and a full index greatly add to the value of 
the book as a useful work of reference. 
ALFRED R. WALLACE 
