344 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



the orifice is found which was observed by M. Lacaze-Duthiers. Un- 

 fortunately, the first series of sections very plainly showed the longitu- 

 dinal cleft near the nervous commissure, which goes from the branchial 

 ganglion to the branchiae, the opening observed by M. Lacaze-Duthiers; 

 but the series of sections was interrupted before this opening was pro- 

 longed into the genital canal. In another series, each preparation con- 

 tained a section of the genital canal, which, however, resembled in every 

 respect the branches (ducts) of the reproductive organ, but of which the 

 special value was not recognized by me. It was from this that I was led 

 to doubt the accuracy of the observation of M. Lacaze-Duthiers. 



The investigations of the past summer demonstrated to me that it 

 was not M. Lacaze-Duthiers, but myself, that was in error. The longi- 

 tudinal cleft is prolonged as a duct, which is nothing else than the genital 

 canal; this canal commences to branch very near its external orifice; 

 these are the branches, which again divide and spread over nearly the 

 whole surface of the body. 



There is no trace of a genital papilla ; the position of the genital 

 opening is exactly the same on either side of the body, and it is also 

 this same opening which serves for the organ of Bojanus; thus it is 

 necessary to regard it as the urogenital opening. The efferent canals 

 of the genital organs and the organ of Bojanus meet together near 

 the common opening. We are, therefore, able to assert, with the same 

 right that the efferent duct of the organ of Bojanus ends at that of the 

 genital organ, or the contrary. Analogy has forced us rather to accept 

 the latter view. 



On the organ of Bojanus of the oyster, the literature is silent. In 

 the excellent work of M. Lacaze-Duthiers (Ann. des Sciences Nat., 4 e 

 s6r., t. IV, 1855) the common oyster has not been studied in this regard, 

 and Von Jhering in 1877 (Zeitschr. Wiss. Zool.), in reviewing what ln?d 

 been published upon the organ of Bojanus in the mollusca, states that 

 our knowledge is null upon this point as regards the oyster. My re- 

 searches also led me to study this organ. 



The organ of Bojanus is not developed as a very clearly marked 

 structure ; it is composed of membranous folds communicating with 

 each other and with a cavity paved with ciliated epithelial cells, itself 

 opening by a fine canal in the urogenital orifice. The cells of the wall 

 of the canal are provided with vibratile cilia longer than those of the 

 cells of the cavity. This cavity appears to be the same as that which, 

 in the mussel, has been called the collecting canal by M. Sabatier. In 

 the wall of this cavity commences a straight canal, which is continued 

 nearly parallel to the genital duct and ends by opening into the so-called 

 pericardiac cavity. This canal is clothed by cells bearing very long 

 vibratile cilia which meet in the center and guard the passage against 

 any object no matter how small. The membranous folds of the organ of 

 Bojanus extend on to the walls of the pericardiac cavity, and upon the 

 posterior part of the sides of the body, then into that part of the mantle 



