^ 



404 BULLETIN OF THE UNITED STATES FISH COJLMISSION. 



the United States and Maryland Fish Commissions to introduce the most 

 approved French metliods into the waters of Maryland and to supple- 

 ment these by even more advanced methods, if practicable. The results 

 of the observations and experiments of the writer during the last two 

 years have been embodied in part in a report to the Maryland commis- 

 sioner for the year 1881, which has been favorably received. Addi- 

 tional papers have been contributed for the same report for 1882, and 

 to the bulletin of the United States Fish Commission, bearing mainly 

 upon the anatomy, finer structure, and development of the animal. An 

 imperfect list of the published works on the subject has also been com- 

 piled by the writer; a more complete catalogue of the literature of the 

 subject in all languages will shortly be published by the Dutch Gov- 

 ernment. 



What has already been put upon record it will not be worth while to 

 discuss, and we will therefore recapitulate only where necessary, adding 

 sundry new facts not yet recorded. To our knowledge of the early de- 

 velopment of the animal we have added nothing. The account given 

 by Brooks for the American, by Salensky, Gerbe, Fischer, and Davaine 

 for the European, species, with little qualification, remains the same. 

 The detachment of the ring or crown of vibratory filaments or cilia from 

 the embryo oyster as asserted by Davaine has not been confirmed by any 

 other observer. Hatschek has lately contributed some valuable re- 

 searches in regard to the development of young bivalves. Working, 

 however, upon the embryo ship- worm, his studies have no direct bearing 

 upon the oyster, but they nevertheless throw considerable light upon 

 the mode of development of the gills, upper gill cavities, liver, muscles, 

 foot and nervous system of the great group to which both belong. This 

 last research shows that the conversion of a part of the velum or ciliary 

 crown above the mouth into palps and gills, as held by Lankester, 

 does probably not take place. The occurrence of ciliary bauds running 

 from the edge of the mantle on its inner side to the mouth, as observed 

 by the writer in spat one-eight of an inch in diameter, was supposed 

 at first to confirm Lankester's view, but Hatschek's researches have 

 made such an opinion untenable. The physiological function of the 

 bands was, however, clear ; by the vibration of the filaments compos- 

 ing them they establish currents towards the mouth, which hurl the 

 food of the young spat into its spacious throat, serving in part the same 

 purpose as the velum adjoining the mouth of the fry. 



Brooks has represented the freshly laid ova of the oyster with a spheri- 

 cal nucleus and nucleolus ; the former is large, clear, and spherical, 

 and is embedded near the center of the ^g^-^ the nucleolus is situated 

 inside of the nucleus in a somewhat eccentric position. I do not find 

 the latter spherical, but formed as if composed of a larger and smaller 

 highly refringent pair of spheres partly fused with each other, or of the 

 same form as the nucleoli of the eggs of Anodonia, as described by 

 Flemming, and somewhat similar to those of the slipper limpet {Cre]^i- 



