32 



than others. At its sides run the salivary gland 

 ducts already mentioned. They arise in the large 

 salivary glands, compact bodies of a yellow colour, 

 which are situated asymmetrically about the alimentary 

 canal and nerve collar. The latter is hidden com- 

 pletely except from below. The left gland lies more 

 posterior and more dorsal than the right, and thus covers 

 part of the latter. The ducts are formed by numerous 

 small branches joining up in the tissue of the glands 

 and leaving them dorsally (PI. II, fig. 12, Sal. gl.). The 

 histological structure of this organ is given below. 



Neither gland alters its position during the evagina- 

 tion or invagination of the proboscis, and a further most 

 important point to notice is that neither salivary duct 

 passes through the nerve ring. 



This is probably due to the fact that with elongation 

 of the proboscis the salivary glands came to lie in front 

 of the nerve collar. With the later elongation of the 

 salivary ducts the salivary glands came to lie behind the 

 nerve collar and moved to the position externally to the 

 collar. This explains the fact that in the Pachiglossa 

 the ducts do not penetrate the nerve collar, a feature 

 otherwise common in the Monotocardia, where the glands 

 are posterior to the nerve ring. 



A little distance behind the nerve collar a narrow 

 tube opens into the oesophagus on its dorsal surface 

 (fig. 12). After running forwards for a few millimetres, 

 it curves round and widens into a very thin-walled bag, 

 usually flattened, and of a brown colour in fresh 

 specimens, owing to the contents. The bag extends back 

 for some distance, lying upon the oesophagus. It is the 

 so-called gland of Leiblein (PI. II, fig. 12, Ln. g.) — the 

 poison gland of the Toxiglossa. 



Both gland and oesophagus move over towards the 



