18 AMERICAN JOURNAL 



of mere anatcmy^ almost considers the shell of Mollusks as if it 

 did not exist, at least scientifically. It sees nothing and will see 

 nothing beyond anatomical characters, forgetting that these 

 characters, which in minute animals are often difficult to observe, 

 do not always present a degree of sufficient certainty, and that 

 in microscopic observation there is often more of imagination 

 than would be supposed at first sight. 



In proof of our assertion, we shall state some of the differences 

 between anatomists, concerning certain minute portions of the 

 inner organization of Mollusks, and the numerous errors which 

 have been made on this point, not only by naturalists of ordinary 

 talent, but even by eminent scientific men. 



We shall not now proceed with severity against this school, 

 whose deep studies we admire, and whose discoveries we appre- 

 ciate when they are genuine, but whose exclusive and rather 

 narrow minded spirit we reprove. 



We shall only quote, as an example of the exaggerations to 

 which in matters of classification preoccupations too exclusively 

 anatomical lead, the introduction of the Dentalium into the 

 acephalous mollusca, proposed a few years since by Mr. Lacaze 

 Duthiers, disregarding the rudimentary head of these animals, 

 their lingual dentition, their embryology and their shell, perfectly 

 univalve, which is, after all, but the exaggeration of the typical 

 form of Patella and Fissurella. 



Naturalists of'the second school have devoted their attention, 

 to make it the base of a system of classification, to the thorough 

 study of the differences presented by certain parts in the organi- 

 zation of Mollusks but little known before their researches, and 

 generally considered by their predecessors as secondary and of 

 little scientfic value. Thus, for example. Dr. Pfeiffer has made 

 a very ingenious use of the differential characters of the oper- 

 cula to establish divisions in the operculated terrestrial Pulmoni- 

 fera, which he designates Pneumonopoma. It is thus again 

 that Mr. Loven, after elaborate researches on the lingual denti- 

 tion of Mollusks, a subject but very little known before his time, 

 thought himself justified in adopting, as a basis for the classifica- 

 tion of Gasteropods, solely the modifications presented by this 

 portion of their organization. After him, Mr. Troschel advanced 

 yet further in this path. In a very interesting work, as 

 far as the number and novelty of scientific documents which it 

 contains is concerned,* he made known the lingual dentition of 

 a considerable number of Gasteropod Mollusks, and has taken his 

 observations as a starting point for establishing a certain number 

 of new divisions. Among the naturalists who, in their works, 



* On " The Jaw of Mollusks," 



