40 NOTES, ETC, OX THE AUSTEALIAX ROCK OYSTER, ETC. 



oyster embryology are submitted on this occasion for examina- 

 tion, as also living- examples of the embryo at a period of about 

 four hours after artificial fertilisation. The more prominent 

 embryonic phases enumerated in this communication are like- 

 wise diagrammatically illustrated on the accompanying sheet. 



In connection with the investigation of the embryology of 

 the Australian rock oyster recently conducted, I have been and 

 am still carrying out a series of experiments with the view of 

 accurately determining the influence upon the embryonic brood 

 that is exercised by the advent of fresh water floods or other 

 sudden changes in the salinity of the water. Some of the 

 results already obtained are of a highly interesting and instruc- 

 tive nature. From a series of oysters recently purchased in 

 the market a fully matured male and female were selected for 

 experiment. Portions of milt and ova from these two indi- 

 viduals were abstracted and commingled under precisely the 

 same conditions and placed respectively in water of three different 

 degrees of salinity. The first admitted was placed in sea water 

 of the full ordinary strength. In the second there were equal 

 proportions of salt and fresh water, and in the third one part of 

 salt water to three of fresh. As a result, the ova placed in the 

 equal admixture of salt and fresh water exhibited active vitality 

 and were quickly speeding on their developmental career. Of 

 the ova placed in pure sea water but few were fructified, and 

 these developed very slowly. Those finally placed in the water 

 containing only a one-fourth proportion of sea water were 

 entirely deprived of life and soon commenced to disintegrate. 

 This last-named circumstance suffices to indicate the pernicious 

 effect upon breeding oysters that may be exercised by heavy 

 floods, and opens out a wide field for further investigation. 



It is worthy of note, in association with the embryological 

 details here recorded, that matured ova and sperm-cells were 

 found abundantly developed in individual oysters with shells 

 measuring as little as half-an-inch in diameter, and whose age 

 would not exceed three or four months. This precocity in the 

 reproductive faculties of the species furnishes a clue to the 

 extraordinary rapidity and abundance with and in which the 

 Queensland Rock Oyster seizes upon and spreads itself over 

 every surface presented that possesses favourable conditions for 

 its attachment. 



