BULLETIN OF THE UNITED STATES FISH COMMISSION. 341 



are of a rotatory, gyratory character; at times they turn about a point 

 as upon a pivot; at other times they change place rapidly and traverse 

 the field view in which they are observed. 



The shell is formed about the sixth or seventh day after impregna- 

 tion. 



Artificial fecundation presents no difficulties, and results four times 

 out of five in the formation of mobile embryos, if good spawn is used. 

 Oviposition proceeds gradually in the Portuguese oyster, and some- 

 times for several weeks. When the genital gland becomes transparent 

 at one point it shows that the sexual products are ripe, and that they 

 may be used to advantage. 



Because of what has just been said, and in view of the exceptional 

 fecundity of the oyster of the Tagus* [0. angulata], we have attempted 

 to make some practical applications. With this object, we have ar- 

 ranged at Verdon a claire of 100 square meters in area, into which we 

 have poured the animated products of diverse artificial fecundations. 



The difficulty to be overcome was to prevent the escape of the embryos 

 and assure the renewal of the water. We have attained these ends by 

 making the water pass in and flow out through a bed of fine sand. 



After a month of repeated experiments our efforts were crowned 

 with success. We have had the satisfaction to find some spat fixed 

 upon each of the tiles placed in our experimental claire. This is all 

 the more remarkable, since, up to this time, the past week, there has 

 been no spat attached to the innumerable collectors immersed upon 

 the oyster banks of the Giroude — that is to say, in the very center of 

 the reproductive area. 



A HVBRID PLAICE-PLATE8SA VULGARIS WITH RHOMBUS OTAXI- 



JMUS.t 



By K. E. II. KRAUSE. 



On the 21st day of August, of this year, a remarkable -looking plaice 

 was shown to me, and the question arose whether it was not a turbot. 

 It had been sold by the fish woman Havernick of Warnemunde together 



* One cubic centimeter of the ovary contains : 



Eggs. 



By the method of dissociation 2, 500, 000 



By the method of sections 5,200,000 



Mean 3,850,000 



The volume of the ovary of an oyster, of medium size, varies between 6 and 8 cubic 



centimeters. 



t Ein Schollen-Bastard. Platessa vulgaris X Rhombus maximus. K. E. H. Krause, in: 



Archiv des vereins der Freunde der Naturgeschichte in Meckleriberg (1881). May, 1882, pp. 



119-120. Translated by H. G. Dresel, U. S. N. 



