Fig. 1. View of right side of embryo about six davs old. m niniitli • v 

 vent: /, right lobe of liver; vl. velum. " ' ' 



Fig 2. Older larva of European oyster, Oatrca lurida. L, shell; h. hinge; 

 r? and ri, retractor muscles of the velum, vl ; a, stomach ; i, Intestine; am larval 

 adductor muscle ; b. body cavity. Other letters as in the pre.edinu 

 ». n^'V'- 3. Attached spat of Oatrca virginica. S. shell of spat with larval 

 shell, L. at the beak or umbo ; p. palps; o. gills; c, diagrnmmatir representation 

 of a single row of eillla extending from the mantle border lo the mouth; t/i ; 

 r, radiating muscle fibres of mantle; /, rudimentary tontaoles of mantle border- 

 M permanent adductor muscle; C. cloaca; ve and au, veiiiricle and auricle of 

 the heart; ;/. posterior extremity of the gills and Junction of the mantle folds 

 Other figures as above Compare this figure with PI. I Fig 1 

 Fig. 1 after W. K. Brooks KIg 2 after Thomas H. Iluxlev. Fig 3 after 

 John A. Ryder. 



