FI<II)Tll|OK OKI. AND. M.-X. Kl. 



weaker tissue. This must be done under a dissecting microscope (such 

 as the "Lupenmikroskope" from Leitz) which I believe to be almo.st in- 

 dispensable in all these anatomical studies. The jaw is mounted like an 

 ordinary microscopical preparation, Iml in glycerine jelly instead of Canada 

 balsam. 



To ol)tain the radula, the tniccal mass is placed for some time in a 

 strong solution of caustic potash or sodium (KOH or NaOH); the destroyed 

 mass is placed in water, and under the dissecting microscope the radula is 

 cautiously cleaned, to be later mounted in glycerine jelly. 



The anatomical illustrations were drawn by the help of a camera lucida 

 (except figs. I, I o and 12), those of the radula by the aid of a Reichert 

 microscope (obj. 6, oc. 2), and in the case of the jaws a Leitz microscope 

 (obj. a.,, oc. I or 4). Miss Ræder, designer at the Zoological Institute of 

 the University, lined in and shaded the figures. The water-colour pictures 

 are from the skilful hands of Miss Mørch, designer at the Anatomical In- 

 stitute; only Arion intermedins was drawn from alcoholic specimen, the 

 others from livine animals. 



