ARTIFICIAL PROPAGATION OF OYSTERS. 11 



ORATION. 



iKration as a means for producing conditions favorable to the 

 development of the eggs and larvae was tested out in many experi- 

 ments. Apparatus of many designs with varying degrees of aera- 

 tion proved useless when tried out with the young oysters at every 

 stage of development. It was hoped to carry the minute embiyo 

 oysters through the first stages in water that was purified and 

 agitated by compressed air, as the filtros blocks were not fine enough 

 to restrain them until they had developed shells, but their develop- 

 ment in aerated water was slow and generally resulted in an early 

 death of the embryos or produced shell forms of such decreased 

 vitality that they lived only a short time. Winslow's experiments 

 in 1822 to oxygenate the water by aeration likewise proved unsuccess- 

 ful, and this factor as a necessary step to success is questionable. 



RUNNING WATER. 



The most important result of the summer's investigation into the 

 controlling factors necessary for success in artificial propagation 

 is that oyster eggs and larvae will develop and grow in salt water 

 aquaria as fast and as vigorously as they will in nature if supplied 

 with running roater. The first batch of spawn placed in the un- 

 seasoned apparatus was given a constant supply of water from the 

 beginning in spite of the fact that many got around the filters and 

 were lost. They developed normally from day to day and " set " 

 with practically no mortality 15 days after spawning. In the suc- 

 ceeding experiments the water supply was diminished and every at- 

 tempt made to retain all of the larvae, with the result that stagna- 

 tion and fouling occurred and all of the forms died. The next suc- 

 cessful experiment was accomplished by providing a good supply 

 of running water and would have yielded a greater crop of spat 

 had it been possible to prevent the soft embryonic forms from pass- 

 ing through the filters. 



By introducing the water into the rearing tanks in fine jets it was 

 easy to produce a circulation and agitation throughout the tanks 

 similar to that found in nature. For carrying the embryos through 

 to the shell stage, a glass rod agitator proved effective for use with 

 a very slight flow of water. This prevented a heavy loss of the 

 forms up the shell stage but was not perfected in operation until 

 September, when it became too cold to conduct the experiment 

 further. 



FILTRATION. 



Oyster eggs and embryos are so extremely small that they will 

 pass through felt or the finest bolting silk and consequently it can 

 readily be seen that it is a difficult problem to create a flow of water 

 and at the same time prevent the passage of such minute organisms. 

 A method for accomplishing this was not found until the first week 

 in September, when thousands of healthy straight-hinge larvae were 

 produced but could not be reared to setting size because of the cold 

 weather when water temperatures dropped overnight to 50 and 54° 

 F. and soon killed them. 



The apparatus that solved this perplexing problem consisted of a 

 half barrel equipped as shown in Figure 6. The filtros plate was 



