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Altrices is the name given by Sundevall (K.
Vet. Acad. Handl.
1836, page 64) to his first section of the Class
Aves,
comprehending
those which "alunt pullulos" (feed their young), founded on the
scheme of Oken (Lehrb. d. Zoologie, page 371), in opposition to
Praecoces, the birds which at birth are more or less able to feed themselves,
but subsequently abandoned by its inventor (Tentamen,
p. XX., Nicholson's
transl. p 26).
The division of the Class thus indicated has under
various names been advocated by several authorities, and at first sight
has a plausible appearance; but investigation shows (it has been argued)
that it cannot be adopted. Doubtless the original Birds, like Reptiles,
were Praecoces, and the Altrices are of later date. The existence
of the numerous intermediate forms may thus be explained; but it follows
that we cannot use as absolutely valid differentiating characters such
as are afforded by the open or closed eyes of the young at birth, by their
being clothed in down or naked, by their remaining in the nest or not,
by their way of feeding themselves or being fed. It is possible that the
transition from Praecoces to Altrices has been governed by
purely external circumstances, which may still be in action-such, for instance,
as the nest being built high above the ground or water. There are many
Altrices
whose
whole anatomical structure proves them to be more nearly related to certain
groups of typical Praecoces than they are to other Altrices.
These
circumstances as fully explained (Jenaisch. Zeitschrift, 1879, p.
385, and Bronn, Thierreich, Aves. p. 701) lead to the following
divisions of birds in regard to their development:-
1. Praecoces or Nidifugae
Hatched with eyes open; thickly clad in down;
able to run at once, or almost at once; and having such an amount of yolk
stored in the abdomen as to render them for some time more or less independent
of other food.
Birds in this division:
Ratitae
Crypturi
Gallinae
Laridae
Limicolae
Pteroclidae
Grallae
Anseres
Pygopodes
2. Altrices or Nidicolae
a. Lower
Nidicolae
Some hatched
with their eyes open, others blind; covered or not with down; unable to
leave the nest ; fed by the parents; amount of food-yolk very limited:
Birds in this series
-
Spheniscidae
-
Steganopodes
-
Tubinares
-
Herodii
-
Pelargi
b. Higher
Nidicolae
-
Hatched in a helpless
condition, blind; mostly naked, and for a long time nursed in the nest,
the food - yolk having been used up at birth:
The two series a
and b stand
phylogenetically parallel to each other.
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