346 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



veinber 30, 1882, I described this organ in the following terms: "Be- 

 sides, no anatomist, to my knowledge, has very definitely located the 

 organs of Bojanus or quasi-renal apparatus of the animal, or indicated 

 the apparently close relation of this paired organ to the openings of the 

 generative ducts. It is true these structures are very rudimentary, 

 but seem to be present in a slightly developed condition, in somewhat 

 the same relation to the great adductor as in Pecten, only that they lie 

 close against the mantle at" either insertion of the muscle and on its 

 ventral side. Their extent is sometimes marked by brownish tissue in 

 their walls." 



In order to see these structures at all it is necessary to open the ani- 

 mal with the greatest possible care, in order that the mantle and the 

 underlying delicate tissue of the organs of Bojanus which lie close 

 against the lower side of the muscular insertion be not lacerated be- 

 yond recognition. The body-mass, which is prolonged backwards below 

 the adductor and containing the first bend of the intestine, lies just be- 

 low the organ, and in fact a suspensor membrane connects the two. 

 This suspensor has the same structure as the mantle. The form of the 

 organ of Bojanus in the oyster, taken as a whole and viewed from the 

 side, is somewhat sickle-shaped, and clasps the opposite ends of the ad- 

 ductor next the mantle on either side for an extent of about three-quar- 

 ters of an inch, and rarely extends a very little way forward upon the 

 floor of the pericardiac chamber. In section through its most enlarged 

 part it is somewhat triangular or trihedral, and its inner non-canalicu- 

 lated portion involves more or less completely at this point the parieto- 

 splanchnic ganglia, as is shown by my sections. It is a paired organ, 

 and the portions of opposite sides are about equally developed. Their 

 dimensions, as compared with the same organs in Unio, are very meager 

 indeed. 



When examined under the microscope, sections from the mid-region 

 of the organ show several large canals, six or seven, the walls of which 

 are clothed with an epithelium provided with very long cilia, which hang 

 freely into their cavities. These larger canals are placed near the center 

 of the trihedral body of the organ. Around the larger canals numer- 

 ous smaller canals and induplicatures of membrane are aggregated, 

 which are clothed with a less conspicuously ciliated internal epithelium. 

 These smaller canals evidently communicate with the larger ones, and 

 are probably the secretory portions of the organ, but no crystalloidal 

 bodies in the form of urates were detected, such as may be seen in the 

 renal organ of Arcapexata, for example. The smaller ducts and canals 

 of the organ encroach upon the connective tissue of the adjacent portion 

 of the mantle to some extent. The color of the tissue of the organ in 

 life is frequently dark-brown, so that its extent may be clearly made 

 out in an oyster which has been very carefully opened. Oftener, how- 

 ever, the organ can scarcely be distinguished from the neighboring 

 structures, except by its richer yellowish color. Its greatest develop- 



