122 MOLLUSCA. 



The general arrangement of the alimentary canal is well 

 shown by a median sagittal section of a preserved specimen. 



The brownish digestive gland, commonly called the ''liver,'' 

 will be seen surrounding a portion of the stomach. 



The enlargement on the intestine in the posterior portion of 

 the pericardium is of unknown function. In some forms a special 

 diverticulum from the stomach bears a transparent cylindrical 

 rod, the crystalline style. This can easily be found in Mya. 

 Probably all lamellibranchs have similar structures more or less 

 well developed, but many do not have special pouches for their 

 formation. 



Draw the alimentary canal. (This may be included with 

 your sketch of the nervous system.) 



Cut a preserved specimen into transverse sections about a 

 quarter of an inch thick, and place the sections in their proper 

 order and position. (They should be placed in a dissecting pan 

 in a very little water.) 



Study these sections for the arrangement of organs. The 

 relation of the gills to the branchial and the cloacal chambers 

 should be understood. 



Make drawings of sections that pass through the heart and 

 through the posterior adductor muscle. 



Belding: A Report upon the Quahog and Oyster Fisheries of Massa- 

 chusetts. Fish and Game Com., Mass., 1912. 



Howard and Anson: Phases in the Parasitism of the Unionida?. Jour. 

 Parasitology, 9, 1922. 



Lefevre and Curtis: Studies on the Reproduction and Artificial Propaga- 

 tion of Fresh-water Mussels. Bui. U. S. Bur. Fish., 30, 1910. 



Nelson: On the Origin, Nature, and Function of the Crystalline Style of 

 LameUibranchs. Jour. Morph., 31, 1918. 



: Recent Contributions to the Knowledge of the Crystalline Style of 



Lamellibranchs. Biol. Bull, 49, 1925. 



Smith: The Mussel Fishery and Pearl-button Industry of the Mississippi 

 River. Bui. U. S. Fish Com., 1898. 



If time permits, it will be desirable to become acquainted with 

 some of the structures of theoretic importance and with some 

 of the adaptations of lamellibranchs for the lives they live. For 

 this purpose a few forms have been selected, and directions for 

 the study of the particular parts in question are given. 



