178 HUGH WATSON. 



(PL IX, figs. 27-29, and PI. XXI, figs. 129-132). In A. 

 burnupi and A. sexangula the glands are separate, but 

 they are joined to each other by blood-vessels in such a way 

 as to suggest that they may possibly have been more closely 

 united in the ancestors of these species (PI. IX, figs. 30, 31, 

 and PL XXI, figs. 133, 134). The glands are never united 

 underneath the crop, as in many of the Ole acini dte, but 

 remain widely separate below (PL XV, fig. 78). 



The salivaiy ducts are long and very slender, and discharge 

 into the buccal mass on each side of the opening of the 

 oesophagus. The structure of the ducts is shown in PL XXII, 

 fig. 138. It will be seen that the epithelial cells are of a 

 peculiar shape and provided with long cilia. The epithelium 

 is immediately surrounded by a layer of circular muscles, and 

 outside these there is a layer of longitudinal muscles in which 

 is embedded the salivary nerve. Within the gland the duct 

 splits up into numerous branches, and in these also the 

 epithelium is surrounded by circular muscles. One of these 

 branches is shown in fig. 139, which also shows the appear- 

 ance of the glandular cells of which the gland itself is almost 

 entirely composed. 



The Liver. — The greater part of the posterior half of the 

 body-cavity is occupied by the liver or digestive gland (PL 

 IX, figs. 27-31). In Apera gibbonsi, A. parva, A. 

 burnupi, and A. sexangula the liver consists of two very 

 distinct divisions, one anterior, dorsal, and to the right, the 

 other posterior, ventral, and to the left (PL XXI, figs. 129- 

 131, 133 and 134). Not only do these divisions discharge 

 their secretions iuto the alimentary canal by quite separate 

 ducts, but they are supplied with blood by different arteries, 

 the right division being supplied by one or two branches from 

 the anterior aorta, while the left division is supplied by the 

 so-called posterior aorta. The right division of the liver is 

 divided by the intestine into three main lobes, one lyiug 

 within the anterior loop of the intestine, another in front of 

 it, and the third behind it, as shown in the figures. Of these 

 the anterior lobe, lying above the hind end of the crop, is the 



