JOURNAL OF THE [January, 



HORN AND EYE OF ARION. 



BY LUDWIG RIEDERER. 

 {Read January 2ist, 1887.) 



Arion, Lam. is a slug or snail without shell, respiring by means 

 of lungs. It belongs to the class of Gasteropods, Mollusks. 



Like all nude snails it carries the eyes on the end of the two 

 longer ones of their four tentacles or horns. 



The horn is simply a continuation of the skin. By contraction 

 of muscles extending from the muscles of the foot, right up 

 through the horn to the base of the eye, this can be retracted 

 very suddenly, deep into the body, while the horn in like way is 

 turned over inward. 



On the end plate of the horn, between epithelial cells singu- 

 larly formed, is found an accumulation of sensitive cells, most 

 likely for the sense of touch. 



The eye is of the plain type, and corresponds to a Camera 

 obscura of spherical shape, with Iris, a globular lens, retina, 

 opposite to the side giving entrance to the light, and choroidea 

 with pigment of black color enclosing the whole enclosed surface. 



The method to prepare cuts for microscopical observation 

 and of durability for longer time, consists in putting the (while 

 extended) freshly cut horn in aqueous saturated solution of Cor- 

 rosive Sublimate, during twenty-four hours for fixing. After this 

 it is hardened by 95 per cent, alcohol. Another way is to fix 

 first by immersion in solution of Osmic Acid of o. i percent, for 

 ten minutes, and to harden after in solution of Bichromate of 

 Potash of 2 per cent, during twenty-four hours. After extracting 

 with water it is brought in diluted alcohol, increasing the 

 strength of this slowly till alcohol absolute. 



Treated in one of these two ways it is in the known way trans- 

 ferred in Chloroform and Chloroform-Paraffine. 



The cuts fastened to the slide may be tinted by some of the 

 solutions of Carmine, Haematoxylin or Safranin (and enclosed), 

 to make more distinct the different tissues. 



