328 DR. GADOW ON THE ANATOMY OF PTEROCLES. [Mar. 2], 
exist in our common Pigeon, and thus they are in contrast with those 
birds in which ceca are altogether wanting, like Woodpeckers, Parrots, 
and others. Garrod likewise included the Passerine birds amongst the 
Menotyphla (to use a Heeckelian term for animals possessing ceca). 
Now I think this is not correct ; and we must. consider this matter 
a little further. Garrod himself came to the conclusion that the an- 
cestral bird-stock did possess ceca; as this is undoubtedly true, it 
follows that all those birds which are now found without ceca 
must have lost them, either phylogenetically or even during their 
ontogenetic development. In fact we see, in embryos of such birds 
as have when adult only very small quite rudimentary ceca, 
that these organs are, in the embryo, just as well developed as in 
birds with long czeca; but these cca, in a Pigeon for instance, do 
not grow any further. They are in early life stopped in their deve- 
lopment, and thus remain inarudimentary state. Again, in all those 
birds which are completely devoid of czeca the tendency to suppress 
these organs is simply carried out to the extreme. We cannot, 
therefore, group the birds into birds with ceca and birds without 
czeca ; and this is especially wrong, as there exist many birds which, 
although apparently allied to each other, differ greatly in the pre- 
sence or absence of czeca, 
If we want to take the czeca into consideration at all, we must 
take another point of view: that is, are the czeca of any use to the 
birds in question or are they not? Now, apparently, in all birds 
which have well-developed czeca they are useful, although we must 
confess that we do not know in what way. Again, in birds with 
very small czeca, where these organs are simply vermiform-like pro- 
cesses, and which never contain any chyle in their extremely small 
lumen, they cannot have any physiological function, else they would 
not have been suppressed. 
No doubt in some cases, in which they are not quite aborted, as 
for instance in the Crows and in our common Pigeon, the glands in 
their walls may still produce some secretion, which then may be 
made the best of. But this is one of the cases in which. rudimen- 
tary organs are not completely stopped in their functions although 
they are useless, simply because the animal hitherto has not been 
able to get rid of them entirely: thus, for instance, the appendix 
vermiformis of man, or another example still more striking, our 
thymus gland, which, although a gland, is now without a duct, and 
thus rather a paradox. 
But to return to our question. It is clear that birds with rudi- 
mentary ceeca have to be grouped together with lipotyphlous birds, 
2. e. oirds which have lost these organs. 
The great development of the ceeca therefore constitutes a consider- 
able difference between the Pteroclidze and the Columbide, as the 
former and the Gallinacei are decidedly menotyphlous and the 
Columbe lipotyphlous, 
In the Gallinacei the whole digestive tract always forms four very 
distinct loops: the duodenal one is the first ; the next two loops are 
formed by the ileum ; in birds which, like Perdiz, have a compara- 
