[80] 



H ^l^ctho^ of prcparlno, for fllMcroscopical 



Stu^v^ the IRabula: of Small Species 



of (3a6te^opo^a/" 



By Charles E. Beecher. 



ONE of the early methods employed to obtain the lingual 

 membranes of Gasteropoda was by actual dissection. 

 This process, in many cases, is very laborious and the results 

 unsatisfactory. Advantage was next taken of the resistance of 

 the radulK to the action of ordinary chemical reagents. The 

 resistance to acids and alkalies induced the early belief in the 

 silicious composition of the teeth, and it is only quite recently that 

 the fallacy has been eradicated from text books on natural history, 

 and from special works on the moUusca. It is now known that 

 the teeth are composed of a substance closely related to chitine. 

 Its behaviour under the influence of the ordinary staining fluids 

 used in microscopical work is quite varied and interesting, and 

 affords some points of comparison with true chitine. 



Another method, applied in the study of the extremely small 

 radulge of minute species of snails, was to crush the animal, and 

 examine the dentition through the translucent tissues. Of course, 

 this plan is in itself not altogether satisfactory, on account of the 

 difficulty of distinctly studying the characters of the lingual mem- 

 brane. Besides, it was not conducive to the production of clean, 

 beautiful, and permanent preparations, such as ought to be retained, 

 to serve as the types from which descriptions and illustrations have 

 been made, and from which important deductions have been 

 drawn. 



When the characters of the odontophore came to be studied, 

 it was first thought that they would furnish a simple means of 

 classification, and an infallible method of determination. At the 

 present time, the best authorities have abandoned nearly all the 

 classifications of the Gasteropoda based upon the characters of 

 this member alone, and give to it an importance about equal in 



* Frum The Journal of the Neiv York Microscopical Society. 



