176 HUGH WATSON. 



rather suddenly ; but, as might have been expected, the 

 crop is much more distended in some specimens than in 

 others. 



The walls of the oesophagus and crop are very similar 

 in structure (PI. XV, figs. 78, 79, and PL XXII, fig. 135). 

 The epithelial lining is normally thrown into longitudinal 

 folds, and consists of columnar cells without any cilia. Out- 

 side the epithelium of both oesophagus and crop there are 

 three layers of muscle-fibres. The fibres of the inner and 

 outer layers are longitudinal, Avhile those of the intermediate 

 layer run in a circular direction. 



The Stomach, Intestine, and Rectum. — Beyond the crop 

 in Apera parva the alimentary canal enlarges to form a 

 small stomach, into which the hepatic ducts open (PL XXI, 

 fig. 131). In the other species of Apera (with the possible 

 exception of A. puree Hi) there is no true stomach, but the 

 crop passes directly into the intestine at the openings of the 

 hepatic ducts. 



At first the intestine bends abruptly upwards and towards 

 the right side of the animal. In A. gibbonsi it then 

 describes a curve on the upper surface of the liver like a 

 reversed S (PL IX, fig. 27; PL XXI, figs. 129 and 130). 

 The posterior curve towards the left side is somewhat shallower 

 than that towards the right, and beyond it the alimentary 

 canal continues backwards low down on the right side of 

 the posterior end of the liver. In A. parva the intestine, 

 after curving over to the right side of the liver, passes 

 straight backwards, the second curve towards the left side 

 being absent (PL IX, fig. 28; PL XXI, fig. 131). 



In Apera burnupi and A. sexangula the first curve is 

 much deeper, and forms a loop which extends the whole way 

 down the right side of the liver, in which it is partially 

 embedded (PL IX, figs. 30, 31, and PL XXI, figs. 133, 134). 

 The anterior portion of this loop lies further forward than the 

 openings of the hepatic ducts. The posterior curve is shallow 

 in these species, and the alimentary canal is continued on 

 the right side, as in A. gibbonsi and A. parva. 1'he 



