50 THE AMERICAN MONTHLY [Apr. 



in others and where there is no special need either from 

 habits or surroundings for them we find very primitive 

 organs formed and developed. It will pay to carefully 

 inquire into the existing special conditions which are 

 found in many of these forms and which led the writer 

 of this article to carefully study the make-up of a very 

 common Mollusk found abundantly on the shores of 

 Cape Cod and which is popularly called the "scallop." 

 A cursory observation of Pecten Irradians, or the 

 scallop, with its scalloped edge from which this Mollusk 

 derives its vulgar cognomen and the varied hues of the 

 curved lines on the outside of this bivalve presents a 

 very unique appearance. 



But a view of the hidden beauty which lies within can 

 only be observed after careful study and some pains- 

 taking research. 



There are two great divisions of Mollusca, the Glosso- 

 phora, (Mollusks witli head region prominently developed 

 and always provided with an odontophore or rasping 

 tongue) and Lipocephala, or 3Iollusks with undeveloped 

 head region (acephalous) and which have no cephalic 

 eyes or rasping organs. 



The Pecten belongs to the Family Ostracea which in- 

 cludes the edible oyster and is a division of the Order 

 Monomya which has for its special characteristics the 

 facts that the Anterior Adductor muscle is absent and 

 there is no siphon as is the case with the clam. It has 

 however a large Posterior Adductor muscle which is 

 much prized as an article of diet and to obtain which 

 millions of the mature organisms are yearly sacrificed. 



Again the Order Monomya comes under the class of 

 the Lamellibranchia which may be defined as a Lipo- 

 cephala or acephalous Mollusk having ctenidia or gills in 

 the form of layers disposed sy metrically, two on each 

 side of the bivalve. 



In some Lamellibranchia althoufirh there are no ce- 



