148 
NATURE 
[OcTOBER 2, 1913 
from homologous parts or material, the respective 
modifications may proceed by different stages and 
means, and the ultimate resemblance will be less close 
.and deficient in detail. Such cases are most likely to 
happen between groups of less close affinity, whether 
separated by distance or by time. Homoeo-tely: the 
same end has been fairly well attained. The target 
has been hit, but not the mark. 
Parately.—The feature has been evolved from parts 
and material so different that there is scarcely any or 
no relationship. The resulting resemblance will at 
best be more or less superficial; sometimes a sham, 
although appealing to our fancy. Para-tely: the 
neighbouring target has been hit. 
EXAMPLEs. 
Isotely: Bill of the Ardeidz Balzeniceps (Africa) 
and Cancroma (tropical America). 
Zygodactyle foot of cuckoos, parrots, woodpeckers 
23) 
a 
Patterns and coloration of Elaps and other snakes. 
Parachute of Petaurus (marsupial); Pteromys 
(rodent) and Galeopithecus. 
Perissodactylism of Litopterna and Hippoids. 
Bulla auris of Plioplatecarpus (Pythonomorphe) and 
certain whales; if tympanic=quadrate 
Grasping instruments or nippers in Arthropods: 
pedipalps of Phryne; chelz of squill; first pair of 
mantis’ legs. 
General appearance of moles and Notoryctes, if both 
considered as mammals; of gulls and petrels, if con- 
sidered as birds. 
Homoeotely : Heterodactyle foot of Trogons (34). 
Jumping foot of Macropus, Dipus, Tarsius. 
Intertarsal and cruro-tarsal joint. 
Fusion and elongation of the three middle metarsals 
of Dipus and Rhea. 
Paddles of Ichthyosaurs. Turtles, whales, 
“Wings” of Pterosaurs and bats. 
Long flexible bill of Apteryx and snipes. 
Proteroglyph dentition of cobras and Solenoglyph 
dentition of vipers. c 
Loss of the shell of Limax and Aplysia. 
Complex molar pattern of horse and cow. 
Parately: Bivalve shell of Brachiopods and Lamelli- 
branchs. 
Stretcher-sesamoid bone of Pterodactyls (radial 
carpal); of flying squirrels (on pisiform); of Anoma- 
lurus (on olecranon). 
Bulla auris of Pythonomorph (quadrate) and Wale 
(tympanic); if incus=quadrate. 
“Wings” of Pterosaurs, or bats, and birds. 
The distinction between these three categories must 
be vague because that between homology and analogy 
is also arbitrary, depending upon the standpoint of 
comparison. As lateral outgrowths of vertebre all 
ribs are homogenes, but if there are at least hamal 
and pleural ribs, then those organs are not homo- 
logous even within the class of fishes. If we trace a 
common origin far enough back we arrive near bed- 
rock with the germinal layers. So there are specific, 
generic, ordinal, &c., homoplasies. The potentiality 
of resemblance increases with the kinship of the 
material. 1 
Bateson, in his study of Homeeosis, has rightly 
made the solemn quotation: ‘There is the flesh of 
fishes . . . birds . . . beasts, &c.” Their flesh will 
not and cannot react in exactly the same way under 
otherwise precisely the same conditions, since each 
kind of flesh-is already biased, encumbered by in- 
heritances. If a certain resemblance between a rep- 
tile and mammal dates from Permian times, it may 
NO.' 2292, VOL. 92] 
penguins. 
be homogenous, like the pentadactyle limb which as 
such has persisted; but if that resemblance has first 
appeared in the Cretaceous period it is Homoplastie, 
because it was brought about long after the class 
division. To cases within the same order we give 
the benefit of the doubt more readily than if the 
resemblance concerned members of two orders, and 
between the phyla we rightly seek no connection. 
However, so strongly is our mode of thinking in- 
fluenced by the principle of descent that, if the same 
feature happen to crop up in more than two orders, 
we are biased against Homoplasy. 
The readiness with which certain Homoplasies 
appear in related groups seems to be responsible for 
the confounding of the potentiality of convergent 
adaptation with a latent disposition, as if such cases 
of Homoplasy were a kind of temporarily deferred 
repetition, i.e. after all due to inheritance. This 
view instances certain recurring tooth patterns, which, 
developing in the embryonic teeth, are said not to be 
due to active adaptation or acquisition, but to selec- 
tion of accomplished variations, because it is held 
inconceivable that use, food, &c., should act upon a 
finished tooth. It is not so very difficult to approach 
the solution of this apparently contradictory problem. 
Teeth, like feathers, can be influenced long before 
they are ready by the life experiences of their pre- 
decessors. A very potent factor in the evolution of 
Homoplasies is correlation, which is sympathy, just 
as inheritance is reminiscence. The introduction of a 
single new feature may affect the whole organism 
profoundly, and one serious case of Isotely may arouse 
unsuspected correlations and thus bring ever so many 
more homoplasies in its wake. 
Function is always present in living matter; it is 
life. It is function which not only shapes, but creates 
the organ or suppresses it, being indeed at bottom a 
kind of reaction upon some stimulus, which stimuli 
are ultimately all fundamental, elementary forces, 
therefore few in number. That is a reason why 
nature seems to have but few resources for meeting 
given ‘‘ requirements ’’—to use an everyday expression 
which really puts the cart before the horse. This 
paucity of resources shows itself in the repetition of 
the same organs in the most different phyla. The 
eye has been invented dozens of times. Light, a 
part of the environment, has been the first stimulus. 
The principle remains the same in the various eyes; 
where light found a suitably reacting material a par- 
ticular evolution was set going, often round about, or 
topsy-turvy, implying amendments; still, the result 
was an eye. In advanced cases a scientifically con- 
structed dark chamber with lens, screen, shutters, 
and other adjustments. The detail may be unim- 
portant, since in the various eyes different contriv- 
ances are resorted to. 
Provided the material is suitable, plastic, amenable 
to prevailing environmental or constitutional forces, it 
makes no difference what part of an organism is 
utilised to supply the requirements of function. You 
cannot make a silk purse out of a sow’s ear, but 
you can make a purse, and that is the important 
point. The first and most obvious cause is function, 
which itself may arise as an incidental action due 
to the nature of the material. The oxydising of the 
blood is such a case, and respiratory organs have 
been made out of whatever parts invite osmotic con- 
tact of the blood with air or water. It does not matter 
whether respiration is carried on by ecto- or by endo- 
dermal epithelium. Thus are developed internal gills, 
or lungs, both of which may be considered as refer- 
able to pharyngeal pouches; but where the outer 
skin has become suitably osmotic, as in the naked 
Amphibia, it may evolve external gills. Nay, the 
whole surface of the body may become so osmotic that 
