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Continued from Intestinal Fold or Loop Types
Secondary shortening and widening of the gut (owing
to the assumption of frugivorous habits) may reduce the number of loops,
and may render the original arrangement quite untraceable, as in Carpophaga,
Rhamphastus,
and
Manucodia.
When a bird has acquired strictly
piscivorous habits, the gut is considerably lengthened and narrowed and
may, as in Pandion
and in Haliaetus,
render the old formation
quite unrecognizable. These are, however, exceptions, which are not numerous;
as a rule the lengthening of the pre-existing loops and the additional
intercalation of new ones does not disturb the typical formation, but rather
throws interesting lights upon the lines of new departure along which certain
birds have become developed, e.g. the Alcedinidae
from a Coraciine
stock, now modified through the acquisition of carnivorous and piscivorous
habits.
All the Ratitae agree in having the second
loop right-handed, and the third left-handed; this is a feature which occurs
again only in the Crypturi, Gallinae, Opisthocomus, and
in the Cuculidae.
Moreover, as with the exception of the duodenum
none of the loops are closed and well defined, the Ratitae represent
in this respect the lowest avine type.
The Gallinae form a well-defined group.
Lowest among them stand the Neotropical Cracidae, through which
they lead towards the Crypturi. The Gallinae have also
an unmistakable resemblance to Opisthocomus and thence to the
Cuculidae.
The Turnices are traceable to a Ralline
or low Gralline stock, with assumed plaglocoelous characters of the second
loop.
The pericoelous assemblage is large. It is typically
represented by the Wader, of which the Limicolae and the Rallidae
form the principal groups.
The Rallidae with Otis and Grus
are connected with the
Turnices, more distantly with the Crypturi,
and still more so with
Apteryx. Dicholophus is in all points
a Gruine form, like Psophia,
and cannot be separated from them.
Rhinochetus
contains Ralline, Limicoline, and cannot be and Ibis-like
features; the only bird which it resembles somewhat closely in its very
peculiar intestinal convolutions is Podica.
The Limicolae agree with the Laridae,
and also with the
Columbae
in all essential points. Each of
these three groups contains a number of forms which lead in an unbroken
series from the typically pericoelous birds with four alternating loops
to the typically mesogyrous birds. Most Columbae
and
Laridae
are
mesogyrous, but
Sterna and its allies represent pericoelous or lower
forms. Neither granivorous, nor insectivorous, nor piscivorous habits have
exerted any appreciable influence upon their intestinal convolutions, although
of course the stomach and caeca are affected, The presence of the crop
of the Columbae is repeated in the granivorous Limicoline genera
Attagis and
Thinocorys.
Numenius approaches in various ways the
Ibises, whence a continuous line be traced into Platalea and
Phoenicopterus on the one hand and into the
Pelargi proper on
the other.
Rather different from the Limicolae are
the Pteroclidae. They have four hoops, which are all closed, which
are all closed, left-handed,
i.e.
isocoelous, and straight; the
second and fourth loops have their apices turned back, and especially the
terminal end of the second resembles somewhat a plagiocoelous formation.
The Pteroclidae have consequently various points in common with
the Rallidae, Limicolae,
and Columbae.
The Alcidae are pericoelous and strictly
orthocoelous; they agree with the Laro-Limicolae in the configuration
of their first three loops, but they differ from them in the number of
loops, which is at least six, the last three of which are are left-handed.
They approach in this respect the Pygopodes. These (Colymbidae
and Podicipedidae)
shew unmistakable affinities with what may
be called generalized or low Gralline forms; their four or five loops are
closed, orthocoelous, and alternating. The Pygopodes connect the
large assemblage of the Waders with the following congregation, of which
the Herodii, Steganopodes, Tubinares,
and
Spheniscidae
are
all divergent types. A very close connection exists between the
Herodii
and
the Steganopodes,
and this is supported by numerous other characters.
The Tubinares
are in more than one respect the most specialized
outcome of this great collective Order, and reach in the typically mesogyrous
Procellariinae
their
highest development.
The Spheniscidae are very specialized. They
possess undeniable characters in common with the Pygopodes, Steganopodes,
and Tubinares; they are on the whole orthocoelous, but the extreme
length of their gut thrown into numerous straight and oblique, or quite
irregular, convolutions renders comparison very difficult.
The Anseres, to which belongs Palamedea
as a probably very old member, are all orthocoelous and combine pericoelous
and plagiocoelous characters in their second loop. The five or six principal
loops are alternating; the last four are closed and straight. As typically
orthocoelous, aquatic birds, and as Praecoces they agree with the
Pygopodes, and the root of the stock of the Anseres has to
be looked for in this direction alone.
The Pelargi, containing the Hemiglottides
(Ibis and Platalea), Phoenicopterus, and the Ciconiae, are
rather diverging forms, which can be characterized as possessing four very
long and mostly closed loops (with occasional secondary loops intercalated),
of which the first three have a tendency to coil their apical ends into
more or less irregular spirals: this leads sometimes to an almost mesogyrous
formation.
The Hemiglottides approach nearest to the
Limicolae, although their points of resemblance with Numenius
may possibly be cases of convergence only. Very closely allied to,
in fact inseparable from the
Hemiglottides,
and connecting them
with Tantalus, and thus with the Ciconiae proper, is Phoenicopterus;
there is not one single feature in the whole of the Digestive System
in which this bird differs from the Pelargi
or resembles the Anseres
except in the presence of small but functional caeca, which are nearly
lost in the Pelargi. But these caeca stand in direct relation to
the food of the Flamingoes, which consists of the confervae in the mud
of the lagoons. The zoophagous Pelargi have lost them, the phytophagous
Flamingoes have preserved them.
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The Ciconiinae proper, represented by Ciconia,
and connected with the former genera by Tantalus, are essentially
telogyrous ; their second loop is right-handed, and accompanies the duodenum;
this is a rare feature, and is of taxonomic value for the diagnosis of
the subfamilies of the Pelargi.
The Pelargi are often classed with the Herodii,
but these two Families differ from each other in almost every
point of primary importance.
There are also certain resemblances between the
Pelargi and the
Accipitres, the chief connection is formed
by the telogyrous character, the mode in which additional loops of the
lengthened gut are stowed away, and the tendency to convert some or one
of the principal loops into regular spirals. Among the Accipitres, the
Old-World Vultures especially exhibit striking Ciconiine similarities
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The Psittaci are distinctly telogyrous;
all their five principal loops are closed and alternating; this, with the
presence of a crop, and the absence of functional caeca, are features which
occur again together only in the Accipitres. The absolutely vegetable
food of the Parrots would sufficiently account for the differences which
exist between them and the entirely zoophagous Accipitres. However,
this indication of a possible relationship between the Birds-of-Prey and
Parrots is as little binding or satisfactory as other suggestions based
upon other organic systems.
Of the Coccyges the Cuculidae possess
four intestinal loops, of which the first and second are right-handed.
The loops are on the wholr orthocoelous, but the apices of the two middle
ones are often turned up, or the second loop is plagiocoelous. Moreover,
they possess fully-developed caeca. In all these respects they resemble
to a great extent the Gallinae; and this hint is considerably strengthened
by Opisthocomus,
which is, barring special features, exactly intermediate
between the
Cuculidae
and the Gallinae. The Musophagidae
seem to possess but three loops, the original second loop havng been
suppressed in connexion with the frugivorous habits of these birds. The
isocoelous feature of the
Musophagidae
is therefore reduced to a
secondarily acquired one, and to a case of convergence towards the typically
isocoelous birds.
This Pici (Picidae, Capitonidae, and
Rhamphastidae)differ, like the Epopes (Bucerotidae
and Upupidae),
from all the remaining birds in the
alternating position of their four loops, which in the frugivorous Rhamphastidae,
as well as in the extremely short-gutted genus Upupa, are reduced
to three by the suppression of the original second loop. Xantholaema,
one of the Capitonidae,
has this second loop still indicated.
The total absence of caeca in all these birds is a coincidence, while there
are no obvious characters, besides the anticoelous convolutions, which
point to a close relationship between the Pici and the Epopes.
The remaining are all isocoelous. Of them the Coraciidae
standnearest to the hyhypothetical ancestral or central stock, because
they are the most generalized group, from which all others can be derived.
The
Alcedinidae,
which have reached a truly mesogyrous formation,
started in one direction from or out of the Coraciidae.
The lengthened gut of the Kingfishers in conformity
with their generally piscivorous habits, forms a left-handed spiral by
its sccond loop, while the fourth loop is long, and in the more piscivorous
members widely open and irregularly placed. The affinity between the Coraciidae
and the Alcedinidae in opposition to other groups may be expressed
by the term Halcyones.
The Striges verge towards the plagiocoelous
type, but all their affinities rest with the Coraciidae and Caprimulgidae
combined. These three Families possess long caeca; the Alcedinidae,
Cypselidae
and
Trochilidae,
have lost them, the first of these
because of their piscivorous and cancrivorous habits.
The Cypselormorphae (Caprimulgidae, Cypselidae,
and Trochilidae)agree very much with each other. They all have
only three intestinal loops, which are short, in agreement with their principally
insectivorous habits. The
Trochilidae
differ in the possession of
a crop. The
Cypselidae
and Caprimulgidae
are somewhat more
closely related to each other, and the latter (including
Podargus)
turn
towards the Owls. The Cypselidae are sometimes supposed to be somewhat
nearly allied to the Passeres. Their alimentary system does not
altogether favour such a view; but perhaps the ancestors of Colius
once
filled this gap, leaving their existing descendants now in a solitary position..
l
The Trogonidae stand on a lower level than
the Cypselidae, Trochilidae, and Coliidae, on the same level
as the Caprimulgidae
and
Coraciidae,
and connect them all
with each other. The Trogons still possess well-developed Caeca like the
Coraciidae, Caprimulgidae,
and
Striges, while all the other
isocoelous birds have lost them, or have only functionless remnants of
them.
The Passeres are a very uniform group. They
all possess only three loops, without indications of more; the second and
third are left-handed; the second becomes a left-handed spiral, the turns
of which depend upon the length of the gut; the third loop is always open,
and invariably encloses the duodenum between its descending and ascending
branches, the latter branch being situated on the ventral and left side
of the descending branch of the duodenum. This arrangement is invariably
the same, even in the Mesomyodians, and in such otherwise aberrant forms
as Rupicola and Pitta. There is a special line which leads
from the Laniine forms through the Austrocoraces (Gymnorhina, Graucaulus,
Strepera, and Paradiseidae) into the
Coraces
proper,
which latter have produced some special modifications of the intestinal
convolutions, and may be looked upon as the last and highest blossom of
the avine tree.
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