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 Anomalogonatse possess either weil- 

 developed cseca, or a tufted oil-gland, whilst all 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 cseca 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 Todus therefore exactly substantiates what might have 

 justly been inferred a 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 livinff 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 famihes of the Anomalogonatae — 

 as, e. g., the iz'ce/js-slip of the Caprimulgidse, the gluteus quintus 

 of the Coliidae, the vomer and the gluteus primus of several — 

 which are not represented at all in Todus. I'hese 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 Anomalogonatse 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 Anomalogonatse. That one or more of such 

 structures should have disappeared in Todus, 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 som.e 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. 



