196 THE MINUTE ANATOMISTS 



he says discharges a calcareous secretion into the 

 intestine. 



Swammerdam's account of the complicated reproduc- 

 tive organs of the snail is a marvel. If it were now an 

 untouched inquiry, and if a trained naturalist, armed 

 with modern appliances, were to spend a summer in 

 elucidating it, he would do well to turn out so good 

 a history as this. The darts are the only things 

 which completely puzzle Swammerdam, and this is not 

 surprising, for their function is by no means cleared 

 up even now. Only a single blameable weakness is to 

 be remarked ; being unable to explain the spermatheca, 

 he throws out the wholly unjustifiable speculation that 

 it answers to the cavity in which the murex stores its 

 purple dye.^ 



Swammerdam gives a careful representation of the 

 nervous system of his snail, noting particularly the 

 cesophageal ring, which he had found in moths also 

 and all other insects examined by him. He notes the 

 great mobility of the nervous ring upon the oesophagus, 

 and figures the muscles by which its position can be 

 altered. The lateral oesophageal connectives answer, he 

 thinks, to the spinal cord. 



Of the shell he has much to say. It is a tube spirally 

 wound about a small central space, which is sometimes 

 closed in the apple-snail as in many others ; he notes 

 that in Vermetus a number of the spires are unconnected 

 and irregular. In some aquatic snails the shell can 

 be recognised even in the egg. It is invested by a 

 " periosteum." When the snail is about to add to its 

 shell, it cleanses the old periosteum with its mouth, 

 removing pieces and swallowing them ; at these times it 

 remains long motionless. The new shell is formed, 



1 For Swammerdam on the androgyny of the snail see supra, p. 118. 



