INTESTINAL TRACT OF BIRDS. 269 



Charadriiformes. 



IdmicolcK. In the Glareolidse archecentrie ; in tlie Chionidae, Thinocoridse, and 

 Charadriidye apocentric A, but. in some of the latter family apocentric C. In 

 the Parridye, Alcidte, and most of the Larid;e apocentric B and sometimes 

 practically quite absent, but in Sierc07'ariit.s archecentrie. 



PterocletidcB. Apocentric A. 



Columbid(B. In the vast majority apocentric B, occasionally one and very often 

 both absent, but in Columba Jivia and Columba cenas traces of i^^landular 

 structure and so apparently apocentric C. 



CUCULIFORMES. 



Cuculi. Archecentrie to apocentric A in the Cuculidte ; in the Musophagidaj 

 apocentric B, and usually, if not always, quite absent. In the Psittaci 

 apocentric B. 

 CoRACliFORMES. In the Coraciidfe, Momotidae, and Meropidsc archecentrie ; in the 

 Alcedinidoe and Upupidye apocentric B. 

 SttHffes. Apocentric A. 

 Caprimulgi. Archecentrie. 

 Trocjones. Archecentrie. 

 Cypseli, Colii, and Pici are apocentric B. 

 Passerifor:mes. All that I have examined are apocentric C. 



Gadow (i2. pp. 688-693) has made a very careful study of the relations between the 

 character of the c;eca and the nature of the diet, and I have gained further information 

 from Finn (8) and from Evans (7), and from the keepers at the Zoological Gardens as to 

 the diet of birds. There is very far from an exact correlation between the apocen- 

 tricities and particular diets, but there is enough to make it plain that many of the 

 modifications are homoplastic ; that is to say, that they are multiradial apoceotricities 

 on which no argument as to affinity can be based. 



Archecentrie Type. — The diet in these forms is by no means uniform, but there is 

 a preponderance of feeding on insects and caterpillars, grubs, and so forth ; 

 in fact, of what may be taken as more typical rejjtilian diet. 

 Ajwcentric Type A. A very large number of birds displaying much enlarged caeca 

 live on vegetable diet in which cellulose bulks largely, and it is to be remembered 

 that the digestion of cellulose occurs in the large cseca of some mammalia. 

 Apocentric Type B. Carnivorous diet, piscivorous diet, and especially frugivorous 

 diet are specially associated with the degeneration of the caeca to iunctionless 

 vestiges, or even with the complete disajipearance of the cseca. 

 Apocentric Type C. AVhen it is remembered that the vast majority of the I'asseres 

 display this type, and that yet almost every possible form of diet is found among 

 them, it is at once clear that diet is no complete explanation of the character of 

 the ca3ca. I am more inclined to think that type C is to be associated with a 

 high development of the Avian structure, and that it is a peculiar secretory or 

 excretory organ. 



SECOND SERIES. — ZOOLOGV, VOL. VIII. 40 



