536 H. p. KJERSCHOW AGERSBORG 



other glands which in many p i s t h o b r a n c h i a t a enter 

 the buccal cavity, and are sometimes more strongly developed 

 than the salivary glands.' Sedgwick (1898: 371), referring to 

 the same organs, says : ' In addition to buccal glands, some- 

 times found round the buccal opening, there is always a pair 

 of salivary glands opening into the buccal cavity. The buccal 

 cavity leads into the oesophagus which is followed by a dilated 

 stomach, and is usually provided with a caecal appendage.' 

 In M. leonina the glands of the oesophagus consist of a 

 series of small, simple, saccular glands (PL 32, fig. 41, ^S'.^) 

 arranged in rows along each side of the swallowing tube. They 

 open directly into the oesophagus by small crypts (F). Heath 

 (1917: 147) reports that the salivary glands are absent in 

 Chioraera da Hi (s. Melibe leonina), but, of course, 

 he is mistaken about this. The activity of the salivary glands 

 in gasteropods was beautifully demonstrated by Lange (1902: 

 85-153), who showed there is a close relation between the 

 structure of the nucleus and cytoplasm and the physical 

 condition of the organism relative to starving and feeding of 

 the animals. 



(2) The Oesophagus. 



The length of the oesophagus in an animal circ. 10 cm. long 

 is 3 mm. (PI. 32, fig. 36, Oe). The oesophagus itself is simply 

 a narrow part of the alimentary canal between the mouth and 

 the proventriculus. Corrugations, which begin at the lips and 

 increase progressively in the mouth, deepen still more in the 

 oesophagus. The lining is still non-glandular, but the glands 

 in the underlying tissue increase until the anterior part of the 

 proventriculus is reached, when they end quite abruptly. The 

 corrugations of the oesophagus are largely longitudinal, which 

 suggests that the oesophagus is capable of expansion in case 

 the animal swallows some large food particle. In some nudi- 

 branchs, e.g. the Triton iadae, according to Vayssiere 

 (1877), the oesophagus is very long. 



