THE SNAIL 89 



anus towards the foot in the same manner as in streptoneurous 

 gastropods. By this time the chief nerve ganglia have been 

 developed around the oesophagus, and as yet the embryo is 

 symmetrical, and the anus remains in the mid-ventral line. 

 The shifting of the anus to the right side of the body is due to 

 the development and great posterior extension of the foot, 

 which is placed obliquely across the mouth of the shell, so that 

 the latter falls over to the right side, and in course of growth 

 becomes spirally coiled as explained above. 



