450 MR. FORBES ON THE ANATOMY OF THE TODIES. | May 16, 
be adaptive, or more recently acquired—exhibited by its existing 
descendants. As most of the Anomalogonatz possess either well- 
developed czeca, or a tufted oil-gland, whilst a// lack the ambiens 
and accessory femoro-caudal muscles, it may be presumed with some 
certainty that the ancestor of the group generally possessed both 
well-developed czeca and a tuft to the oil-gland—the first having 
disappeared in the Piciformes, the latter in the Passeriformes, and 
both in the highly specialized Cypseliformes: at the same time it 
was destitute of both ambiens and accessory femoro-caudal muscles. 
The existence of T’odus therefore exactly substantiates what might have 
justly been inferred @ priori on purely theoretical grounds ; whilst its 
insular habitat, the small number of species, and their diminutive 
size are exactly what might have been expected of a very ancient 
and synthetic form, which has been unable to hold its own, on the 
larger areas, with more lately developed and highly specialized forms. 
On the other hand, it is not to be expected, on the doctrine of descent, 
that any living form, however synthetic, should be exactly inter- 
mediate between any other two living groups, because it is nearly 
certain to have been modified in some points pari passu with those 
forms to which it (or, rather, its ancestors more or less remote) gave 
origin. There are structures in other families of the Anomalogonatee— 
as, e. g., the biceps-slip of the Caprimulgide, the gluteus quintus 
of the Coliide, the vomer and the gluteus primus of several— 
which are not represented at all in Zodus. These may, of course, 
have been independently reacquired ; inasmuch as, however, they are all 
structures met with in the Homalogonatous birds—from some form 
of which I cannot doubt that the Anomalogonate are descended—it 
is more probable that they have been inherited directly from a 
common ancestor which possessed these along with the other struc- 
tural characters of the Anomalogonate. That one or more of such 
structures should have disappeared in Z'odus, though present in the 
hypothetical common ancestor, is in no way surprising. I submit, in 
conclusion, therefore, 
(1) That Todus is a much isolated form, with affinities to both 
the Passeriformes and Piciformes of Garrod. 
(2) That it cannot be substantiated that Todus is clearly allied to 
any particular living form of these. 
(3) That this view may be most correctly expressed by making a 
group Todiformes, equivalent to Passeri-, Pici-, and Cypseliformes, 
for the sole reception of the genus Todus. 
(4) That in all probability Todus, though in some respects much 
modified and specialized, represents more nearly than any other 
existing form the common stock from which all the living groups of 
Anomalogonatous birds have been derived. 
