206 STRUCTURE OF THE MOLLUSCA. 



much resembling the Botrylli in their internal organization, 

 hut which are united in very great numbers, so as to form 

 a large hollow cylinder, open at one end only, contractile, 

 and swimming in the sea. 



The above account of the Mollusca, chiefly translated 

 from the works of M. Milne-Edwards, a French naturalist 

 remarkable for the extant and accuracy of his investigations, 

 and the clearness and precision of his style, will serve to 

 afford a general idea of the structure and arrangement of 

 these animals. Should one desire to form a more particular 

 acquaintance with them, he has only to examine with care 

 the organs of those species which he may easily procure in 

 any part of the country where he may be placed. A knife, 

 a needle, a small forceps, and a good lens, together with 

 some vessels, are all the apparatus necessary for this pur- 

 pose. The actions of the living animals may also be ob- 

 served, by placing the marine species in salt water, the 

 aquatic in fresh water, and the terrestrial in a glass, or on 

 leaves. The best guides are the works of Cuvier, Blain- 

 ville, Milne-Edwards, and Deshayes. After commencing 

 such an investigation, the student will not likely return to 

 the mere practice of gathering shells, which, however amus- 

 ing to many, is not a very rational or satisfactory employ- 

 ment. 



EXPLANATION OF THE FIGURES. 



Plate XX. fig. 1 Sepia officinalis. 

 a b c, the body enclosed by the mantle. 

 b b, the longitudinal flaps, or fins, 

 c c, the edge of the bag formed by the mantle, 

 t/, the head. 

 e e, the eyes. 



