758 NATURAL HISTORY OF AQUATIC ANIMALS. 



alcohol will abstract the green and spoil in part the effect of the double stain. In making 

 sections, the best ones which I have ever made have been prepared from portions of whole 

 Oysters which had been imbedded in paraffine, the latter substance having in the molten state 

 interpenetrated all the cavities and spaces in the hardened specimen, which had been previously 

 •dehydrated and saturated with oil of turpentine. 



Note on the organ of Bojanus of the Oyster. — In the first part of this paper it is stated that the organ of Bojanns is 

 rudimentary or wanting in the Oyster. This statement must now be modified. Within the past year, M. Hoek, of 

 Leyden, has demonstrated the existence of the organ of Bojanus in Ostrea edvlis, and the writer has shown it to be present 

 in the American species as a crescent-shaped glandular or canaliculated structure lying just below the adductor and close 

 against it, as a paired organ which also extends slightly into the substance of the mantle on either side. M. Hoek has 

 shown that, as in other acephalous moUusks, this organ communicates with the pericardiac cavity and the genital 

 openings. Its function is excretory. 



Valves of the heart. — ^A pair of very distinct valvular folds separates each of the auricles of the heart of the Oyster 

 from the ventricle, opening upward into the latter. They prevent the blood from regurgitating into the auricles, and 

 cause the blood-current to assume one constant direction, viz, from the auricles to the ventricles, and from the latter 

 through the anterior and posterior aortic vessels to the various parts of the body. 



Fixation of the 8po<.^=-Recent studies have led me to the conclusion that the existence of a byssus in the fry of the 

 Oyster is very doubtful, and that fixation is accomplished at a very early stage, possibly twenty-four hours after the 

 embryos commence to swim, by the border of the mantle, as I have endeavored to show in my paper ' ' On the Fixation of 

 the Pry of the Oyster," illustrated with figures, and recently prepared for the Bulletin of the United States Fish Com- 

 mission, where I also show that the beaks of the larval valves are constantly directed one way, and that the hinge end 

 of the larval shell is inclined upward, the free margin of the left larval valve being brought into close contact with the 

 surface to which attachment occurs through the instrumentality of the margin of the mantle. The attachment itself is a 

 very firm one, and consists of the homy matrix of the calcareous material which serves as a cement to glue the free 

 margin of the lower valve of the fry and spat to the surface which has been chosen as a permanent abode. 



