METHOD OF PREPARATION. xlvii 



V. PREPARATION OF LAND SNAILS FOR ANATOMICAL. 

 STUDY. 



Land snails intended for anatomical examination should be placed 

 -when collected in a vessel of water from which air is excluded^- 

 Usually twenty-four hours is a sufficient time to drown the animal, 

 when they may transferred to 50% alcohol and after a day to 60 and 

 then 80%. It is often impossible on account of lack of facilities to 

 observe this rule ; and in such cases the animal may be thrown into 

 about 60% alcohol when drowned. If time or facilities cannot be 

 had for drowning the snails in water, they should be killed by the 

 usual method, by scalding with boiling water, and then placed in 

 spirit not stronger than 60 % . The one process to be avoided is plung- 

 ing the living animal into spirit ; as this causes so much contraction 

 that subsequent work is very difficult. Of course even a badly con- 

 tracted specimen is vastly better than none ; and no malacologist 

 should neglect to preserve some sort of specimen of a species not 

 known anatomically, in view of the present condition of malacology, 

 and the advantage to be gained for science by the expenditure of 

 the small amount of time involved in preserving the soft parts. 



The dissection of land snails is very easy, a shallow vessel with a 

 floor of blackened wax, some small scissors, a scalpel and pins being 

 all the material required. After removing the shell and observing 

 external features, an incision may be made extending from the top 

 of the head backward, laying open the visceral mass. The genitalia 

 will then be seen on the left (the head being toward the observer), 

 the digestive tract in the middle. Each of these systems may be 

 readily removed and pinned out separately for examination. Jaw 

 and radula may be mounted in glycerine jelly in the usual manner. 



NOTE ON NOMENCLATURE. 



The numerous changes from previous usage in generic and sub- 

 generic names of Helices, which have been introduced in this volume, 

 are mainly due to a rigid adherence to the rule of priority. The 

 older generic and subgeneric names were nearly all proposed for 

 miscellaneous and artificial assemblages of species ; and in these 

 cases we are compelled to accept these names in the sense in which 

 subsequent authors understood them and restricted them. For ex- 

 ample : Ferussac's Helicigona comprised all keeled and edentulous 

 Helices ; but as Risso retains under that name only the H. lapicida 

 and H. cornea, we must accept this restriction ; and as cornea was 



