1913-] Ekendranath Ghosh : Mollusca, I. 221 



(3) A single layer of short columnar cells with elongated rod- 

 shaped nuclei. 



The first and second layers may in some cases be fused in 

 adjacent portions of the tube. 



V. Nervous System. 



The nervous system is of euthyneurous type. Like the other 

 species of the same genus, the ganglia are concentrated to form a 

 rectangular mass, with a hole behind the closely apposed cerebral 

 ganglia for the oesophagus and two salivary ducts. The cerebral 

 ganglia are placed on a higher level than the others. The two 

 viscero-pleural and two pedal ganglia form a flattened squarish mass, 

 being only indistinctly separated from one another by a shallow 

 cruciform gioove. The buccal ganglia are placed at their usual 

 position at the junction of the proboscis and the radular sac on the 

 ventro-lateral aspect. The stomato-gastric connectives are very 

 long in correspondence with the protrusible nature of the proboscis. 



VI. Pedal Gland. 



The pedal gland is an elongated tubular body 17 cm. in length, 

 and is situated beneath the ganglionic mass on the dorsal surface 

 of the foot. It extends about one-fourth the length of the body 

 from the anterior end of the foot. The organ is slightly flattened 

 dorso-ventrally towards the base, but cylindrical in the posterior 

 two-thirds The gland opens externally, in the middle line, in the 

 shallow groove between the head and anterior end of the foot. 



Minute structure. — The lumen of the gland is circular in 

 transverse section in the distal two-thirds of its length, but more 

 or less elongated and flattened in its anterior one-third. The lumen 

 is lined by a single la3-er of broadly columnar epithelial cells in the 

 lower third of its circumference, while at the sides they become 

 graduall}^ cubical which again become flattened out at the upper 

 third. Outside the epithelium Hes a layer of connective tissue 

 continuous above with what forms a sheath round the whole gland. 

 In the anterior flattened portion of the gland, the lower half of the 

 lumen is lined by a single la^^er of columnar epithelium, while the 

 upper half is lined by a single layer of flattened cells. Between 

 the epithelial cells are seen the openings of the ducts of numerous 

 unicellular glands, which form the whole mass of the gland. 



The unicellular glands are more or less club-shaped, with wide 

 ducts opening into the lumen of the tube. The granular contents 

 are stained blue with haematoxylin. 



VII. Muscular System 



On the dorsal surface of the foot towards the anterior end is 

 a muscular cushion with strands passing in all directions and be- 

 coming continuous with the musculature of the foot. This cushion 



