ANIMAL REPRODUCTIONS, 287 
¢ diffufed, and the great mufcular power, by 
means of which they contract more forcibly, 
* whenever touched by the knife. 
‘ To facilitate every thing as much as poflible, 
‘in my diffeCtions, I practifed three methods. 
‘ One propofed by the celebrated Swammerdam, 
“ to whom we owe fo much on the fubject, was, 
‘ by allowing the {nails to die in water ; another, 
‘ by taking away the fhell, and thus leaving them 
‘ to perifh ; and a third, by putting them in cold 
“water, and then boiling it a little. By theie 
‘ different methods, they frequently remain with 
“the neck and head, and fometimes alfo the 
‘ horns, ftretched out, in this manner affording 
“ me opportunities for convenient examination. 
¢ When a {nail extended, and carrying along 
¢ its habitation, is viewed, or when dead, in a fi- 
‘ milar pofition, a long neck, terminating in the 
‘head, appears. ‘Two larger and two fmaller 
“horns rife from the head. A minute globe is 
* at the extremity of each ; and in the two larger 
‘is a black point, called the eye. Around the 
* pofterior part of the neck is a circular promi- 
* nence, called the lap or collar ; on the right of 
‘ which appears a hole evidently for refpiration ; 
* and in it the inteftine for difcharging the feces 
‘alfo terminates. A glandular fhagreen kin, 
‘ varioufly coloured according to the different 
~ *fpecies, covers the upper part of the neck and 
* tall s 
