4 INTRODUCTION. 



genera of shells, but have not possessed the necessary 

 industry, or perhaps sufficient courage, to form a new 

 and more natural one, differing so essentially from the 

 long established, and universally adopted system of the 

 most eminent naturalist that has ever existed. 



The Chevalier de la Marck, however, undismayed 

 by the prodigious difficulties he had to encounter, and 

 though, in the midst of his great and laborious enter- 

 prise, unhappily afflicted with the loss of sight from the 

 effects of an inveterate ophthalmia, (a calamity at all 

 times most deeply to be deplored, and, to a naturalist, 

 nearly an insurmountable barrier to success, as his vi- 

 sion should, if it were possible, be microscopic), stead- 

 ily pursued the path he had adopted, and, with a 

 strength of mind but seldom equalled, and a persever- 

 ing industry greatly to be admired, has brought to its 

 completion — L'Histoire des A nimaux sans VertSbres — 

 a work which will remain a lasting monument of his 

 patient and intelligent investigation of a subject not 

 easily understood, and yet more difficult to be ex- 

 plained with any degree of clearness or correctness, de- 

 prived as he was of the most important aid of ocular 

 demonstration, by which he could have pointed out 

 many other of those extremely slight indications, and al- 



