2G8 DE. P. CHALMKHS MITCHELL ON THE 



character of the Cathartidae. However, tliere is yet another condition possible among 

 these reduced CKca. Is'umerous obserAers liaA^e shown that in the cteca of many birds, 

 whether these be long or short, there occur in different regions masses of lymphoidal 

 tissue. Such masses may occur at the apex of long caeca as in the Owls, or in scattered 

 ))atches as in Ducks ami FoavIs, or in concentrated swellings as in Otis. Berry (3) lias 

 )-(>cently shown tliat the occurrence of these lymphoid masses, in concentrated regions 

 I'orming vermiform apjjendices, or in scattered masses, is frequent in Vertebrates, and he 

 suggests that the vermiform appendix of Man is a specialized and not a degenerate 

 structure. The reduced ca?ca of many birds {e. g. Passerines) are quite different from 

 the obviously vestigial caeca that I have mentioned. They are regularly formed, nijjple- 

 like structures, the lumen of \\ hich is grcatlv reduced bv closelv-set villi and folds. In 

 these, small glands and lymplioid tissue are alumdant ; and in the Sparrow I have noted 

 the presence of abundant dark granules which are ajjparently matter in process of 

 excretion. I distinguish therefore in the conditions of the cieca among birds the 

 following : — 



1. Archccentric Character. — Ca^ca large, thiu-w ailed, containing food-material on 



which some process of digestion is taking place, but which may have in addition 

 the beginning of secretory or excretory function. 



2. Apocenfric Characters. 



A. Caeca enlarged, partly digestive, and partly secretory or excretory. 



B. Caeca functionless, A-estigial or absent. 



C. Caeca r(!duced but tiansformed solely to glandular organs, secretory or 



excretory or both. 



•Palamedea. Caeca archecentrie. Chauna apoceutric A. 



IIatiTjE. Ca^cae archecentrie or ajiocentx'ic A. 



CoLYMBiFOKMKS. Archeccntric. 



Spheniscifokaies. Apocentric B. but according to Gadow archecentrie in some. 



Pkocellakiifoumes. Apocentric B, occasionally one only present. 



CicoxiiFOitMES. Archecentrie in the Pelecanidte. apocentric B in ihe Phaethontidic, 

 Sulida^ Fregatidae, and Plialacrocoracidie (in I'lotns one may be absent); 

 apocentric B in the Scopidfe, Ciconiidie, and Ardeidae, in the latter one only as 

 the normal but jiot invariable condition. In the J'hoenicopteri archecentrie. 



Ansekifokmes (excluding the Palamedeida'). Apocentric A, usually Avith large roAvs 

 of glands, hut in Jfergns apocentric B and one occasionally absL-nt. 



Palconifokme.s. Apoccnti-ic B, vestigial with frequent irregularities and absent in 

 Cathaitidae. 



TiNAMiFoitMES. A])oceritiic A, extreme specialization in some. 



(lALLiFORMEs. Apocontric A in (ialli and Opisthocomi ; archecentrie in Turnices. 



■(lUUiFOKMES. In the Kallidae apocentric A; of the (iruida' archecentrie in the 

 Araminte, apocentric A in the others. In the Dicholojihidte and Otididae 

 apocentric A (extremely so in Ot/\s) ; in the P.iiinochetidac archecentrie ; in the 

 Eurypygidte ajwcentric, probably C ; iu the lleliornithidic archecentrie. 



