INTESTINAL TRACT OF BIRDS. 



241 



Laridae, are derivatives of the pattern only slightly modified by increased length. A 

 modification of the Limicoline-Gruiform metacentre is found in many of the simpler 

 Charadriidse such as Numenius, and consists in the gradual shaping of Meckel's tract 

 into three loops and a supra-duodenal loop. Of the three, one is axial and carries a 

 large diverticulum on its distal limb. From this Charadri-Gruiform metacentre one line 

 of progressively increasing apocentricity, consisting chiefly in a lengthening of the axial 

 loop, is attended by degeneration of the caeca ; it runs through Tringa and Hecurvirostra 

 to Scolopax. The Gruiform metacentre is another apocentric derivative of the Charadri- 



Charadriidae 



Fig. 59. 



Uicholophidae 



Otididas 



Charadriidae 



Grumae 

 \ 



Rhinochetus 



Eurypyg. 



Columbidae 



Opisthocomus 



Plerocles 



Charadrndcfc 



Aramidae 



Chiomdab 



Gruiform 

 Metacentre 



Charadri-Gruiform 

 Metacentre 



CEdicnemidas 



/ Glareolidae 

 / / Thinocoridas 

 ///^Parridae 



imicoline- 



Gniifonn 



Metacentre 



Palamedea 

 Archecentre 



Evolution of the Intestinal Tract in the Alectoromorphine Legion. (For Helorornis read Ueliornis.) 



Gruiform metacentre, and is reached by the first three loops of Meckel's tract, including 

 the axial loop, being more clearly marked off and lengthening equally. Most of the 

 Rallidae remain in this condition. The Gruinse are apocentric modifications of it in 

 which all the loops, except that immediately following the axial loop, increase in length 

 individually. The Psophiinae and Heliornithidae are practically unmodified from it. 

 Bhinochetus is modified only in that the first loop of Meckel's tract is represented by 

 two loops, and that the caeca are reduced. Eurypyga is more modified, its apparent 

 simplicity being almost certainly secondary. The Dicholophidae and the Otididse are 

 very apocentric modifications of it, the apocentricity consisting chiefly in the reduction 



