OYSTER CULTURE IN FRANCE. 625 



This operation purges the ova from the impurities 

 which may have become attached, and aids the separation 

 of such ova as may be still glued together. For this purpose 

 the contents of the receptacle are shaken either with the 

 hand or with a pencil, and then the liquid is left quiet. 

 Half an hour or an hour after, the ova which are unchanged 

 are precipitated at the bottom of the mud which remains 

 suspended in the water ; all foreign matter, torn mem- 

 branes, damaged ova, &c., must then be eliminated. This 

 operation of decanting may be repeated with advantage. 



The seminal fluid is obtained by the same means as 

 the ova, but necessitates no preliminary preparation. It 

 is poured on the mud in which the ova are lying, and the 

 fecundation takes place at once.* 



Henceforth the successive phenomena of development 

 can only be observed with a microscope. After coming in 

 contact with the elements the ovum, which at first was in 

 the shape of a pear, by degrees becomes round ; the germi- 

 native organ diminishes, to disappear soon altogether, the 

 polar globule shows itself at a point on the circumference, 

 the ovum divides itself into two, three, four segments, and 

 then into so many that at last it assumes the appearance 

 of a raspberry. To describe clearly these different trans- 

 formations and metamorphoses, drawings will be neces- 

 sary. After incubation for seven or eight hours, according 

 to the temperature,! the embryo becomes agitated, moves 



* From observations made in the laboratory of M. Balbiani by M. 

 Henneguy, the ovum of the angulata appears to be provided with a 

 micropyle placed at the point of severance ; that is, at the end of the 

 pedicule. 



t At Verdon we obtained moving embryos seven hours after fecun- 

 dation, the water being of a temperature of 22 degrees. 



