CECA 69 
silas, Limosa, Scolopax, Parra, Rhinochetus, many Columbe, Acci- 
pitres, and Passeres ; or (b) they are entirely absent, as in many 
Columbz, Psittaci, Musophaga, Corythaix, Pici, Aleedinids, Bucero- 
tide, Upupidee, Colius, Cypselidx, and Trochilide. 
4. Sometimes one cecum remains in a rudimentary condition 
and the other one has disappeared ; this is the rule in almost all 
Herodii and in Procellaria, but occasionally met with in Steganopodes, 
Podicipes, Strepsilas, and in Atrichia. 
The greatest development of the ceca occurs in Struthio, Rhea, 
Tinamus, and Meleagris, their aggregate volume equalling or even 
surpassing that of the rest of the intestinal canal, the czeca in these 
cases, especially in Ratitz, shewing numerous transverse constric- 
tions and sacculations, which increase the absorbing surface. 
A certain correlation exists between the cca and the length 
and width of the rectum. 
The examples enumerated above seem to shew that ceca are 
not required for the digestion of meat, fruit, and grain. Fish-eating 
Ducks have considerably shorter cca than their strictly vegetarian 
relations ; the same remark applies to those Waders which live upon 
mollusks and other soft-bodied invertebrates. On the other hand, 
the well-developed czeca of Coracias, Caprimulgus, Merops, Cuculus, 
and those of the likewise insectivorous Todies and Bee-eaters, make 
it not improbable that in the ceeca not only cellulosis (as in Mam- 
malia) but also chitine is digested. 
Lastly, the presence or absence of the czeca being thus explained 
by the food, a clew will occasionally be afforded to the systematic 
position of birds in which they appear against reasonable expectation. 
It is clear that change of diet may be accomplished in a much 
shorter time than it takes to modify the various digestive organs. For 
instance, the exclusive meat-diet of the Birds-of-Prey has reduced 
their ceca to mere rudiments, and it is more than improbable that 
the insectivorous habits of many of the smaller Falconide will ever 
redevelop these organs, especially since these birds throw out the 
indigestible parts in pellets). Owls now cannot be distinguished 
from Diurnal Birds-of-Prey by their diet ; they possess large ceca, 
and cannot therefore be derived from the Accipitres, which have lost 
them, nor is it probable that Owls and Accipitres came from one 
common stock and are collateral branches, because in this case both 
would be of equal age, and we should have to assume that the meat- 
diet had in one branch suppressed and in the other branch preserved 
or even increased the ceca. We can only conclude that the Owls 
are descendants of a stock of birds which, like the Nightjars, lived 
on chitinous insects (Beetles, Moths), and that they, like Podargus, 
as shown by its predilection for mice, comparatively recently took 
to the flesh of vertebrates. 
As might be expected, the members of any large and much 
