YOLDIA LIMATULA. 107 



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. 



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. 



Belding: A Report upon the Quahog and Oyster Fisheries of Massachusetts. 



Fish and Game Com., Mass., 1912. 

 Lefevre and Curtis: Studies on the Reproduction and Artificial Propagation 



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

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



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



YOLDIA LIMATULA. 



This form belongs to the order Protobranchia, and is supposed 

 to be one of the most primitive of living lamellibranchs. It 

 lives in soft mud, such as is found in quiet coves and bays. 

 (It is abundant in the Eel Pond at Woods Holl.) Although it 

 burrows in the mud, it lives near the surface, and frequently 

 has the posterior end above the mud. 



1. Place a specimen in a dish of sea- water, and notice the 

 movements and shape of the foot. See if the movements are 



