6 INTRODUCTION. 



timately attains its full period of growth and mature 

 completion, affording a convenient habitation and se- 

 cure retreat, or only defending such organs of the ani- 

 mal as the Master Architect of nature had pointed out 

 as being most in need of protection. 



Where an opportunity was not afforded La Marck, 

 orthe persons assisting him in his great task, to examine 

 the anatomical structure of the animal, he has, from 

 analogous reasoning on the muscular impressions of 

 the shells, or other characteristic and concurrent tes- 

 timonies, been enabled to determine with great pro- 

 bable certainty, the most consistent and natural asso- 

 ciation of their several species. In many instances he 

 has beautifully displayed a strong and continued chain 

 of approximation, amounting almost to a positive proof 

 of the transitions which appear to take place from one 

 genus to another, and which some physiologists hypo- 

 thetically assume to exist, firmly linking together the 

 different orders of natural history throughout the cre- 

 ation, by means of those paradoxical and singularly 

 organized animals so frequently met with. 



Awd it may here be observed, that the study of every 



