DIGESTIVE ORGANS. 23 



further at this time : reference to the plates of this and succeed- 

 ing volumes will demonstrate this relationship of shell and 

 animal. 



Neither shall we investigate further the forms of shells or 

 their opercula, monstrosities, etc. All these matters, where 

 general in scope, may well be relegated to an introductory treat- 

 ise on Conchology ; or we may at some future time include them 

 with other particulars of more general than special application 

 in a volume of appendix to this series.* 



Digestive Organs. 



The digestive organs in the Prosobranchiates are well devel- 

 oped. The mouth, which is sometimes in the lower plane of the 

 head, and sometimes at the end of a proboscis capable of protru- 

 sion and retraction, is frequently encircled by an extensible lip ; 

 within, it is often armed with a jaw on either side, and the tongue 

 is usually armed on its upper surface with numerous transverse 

 rows of teeth, constituting the lingual ribbon. The oesophagus 

 is often beset with appendages and salivary glands, and leads to 

 the stomach; whence the intestine turns forward, passing close 

 to the kidney and heart and into the respiratory cavity, the right 

 side of which it traverses and finally empties into the anus. The 

 intestine and often a portion of the stomach is embraced by an 



* Such a volume might embrace the facts of geological and geographi- 

 cal distribution, in addition to the outlines of molluscan structure and a 

 history of classification. One can readily conceive that such a volume 

 would be a natural outgrowth and completion of a monographic series, 

 a collation of the information contained in its predecessors, and an appli- 

 cation of the same to the various important generalities which occupy 

 modern scientific thought. It is a reproach to natural science, and to 110 

 department thereof more than to conch ology, that most of its votaries 

 consider the determination of species and genera its legitimate end ; that 

 they are more actuated by the selfish ambition of acquiring reputation 

 than by the love of knowledge. Thus it happens that in most treatises 

 very few structural details are given, whilst the technical descriptions of 

 external features occupy the bulk of the work such descriptions being the 

 necessary justification for the imposition of generic or specific names and 

 the consequent glorification of the namer. I propose, as far as practi- 

 cable, to reverse this procedure, to consider the necessarily arbitrary and 

 artificial nomenclature simply preliminary ; as a facility towards the ac- 

 quisition of knowledge of nature and its laws not as the end of knowl- 

 edge. As the builder finds it convenient to express the kinds of instru- 

 ments used in his labor, by technical names, so do naturalists find 

 necessary a succinct designation of the subjects of their studies ; and the 



