WV W. SAVILLE-KENT, F.L S., F.Z.S., KTC. 37 



by tLeir active oscillating- and vibratory movements. [Should 

 the sperm cells fail to exhibit this vitality, their admixtiire with 

 the ova -will prove of no avail. 



In practice it will l)e found that the number of oysters 

 containing the female elements or ova is greatly in excess of 

 those producing the milt or sperm cells, the average proportion 

 associated with many hundred examples recently examined being 

 one male to six or seven females. The small quantity of milt 

 that is required to fertilise a very large number of ova satis- 

 factorily explains Nature's economy in this direction. No 

 peculiarities of external structure exist, so far as I have been 

 able to ascertain, that permit of distinguishing between the 

 male and female oyster before it is opened. Healthily matured 

 milt and ova having been successfully obtained, portions of each, 

 the ova predominating, may be mixed in a watch-glass half full 

 of sea water, and well stirred together. The ova, being heavier, 

 will soon sink to the bottom, leaving the spermatozoa dili'used 

 as a cloud through the water. After an interval of ten minutes the 

 top water may be poured oft" or withdrawn with a pipette and 

 fresh supplied, and any fragments of lacerated tissue or tufts of 

 immature milt be removed with a needle ; these, if left, will 

 decay and pollute the water. The pouring-off process should be 

 repeated until the top water is quite clear and the bottom 

 consists entirely of fertilised ova. If a small drop of water 

 containing the mingled milt and ova is examined at short 

 intervals some remarkable changes in the form and structure of 

 the ova will soon l)e observed. 



Almost immediately following upon the admixture of the 

 two elements it will be found that the sperm cells are adhering 

 in numbers by their dilated heads to the delicate capsular invest- 

 ments or vitelline membranes of the ova, and communicating 

 to many of them, through the vigorous vibrations of their tail- 

 like prolongations, a distinct oscillatory motion. It may also be 

 observed that through the aperture of the narrower end of the 

 capsule, known as the micropyle, several of the sperm cells have 

 eft'ected an entrance, and have been brought into direct contact 

 with the body of the ovum. The fusion between the two 

 elements that then takes place is not easy to trace, but the 

 results arising from the union are speedily manifested. The 

 ovum prior to fertilisation was distinguished by the presence of 



