19 



the salinity is to be determined is plaeed in u jur, or one of the 

 special eylinders providtd with the onttit and the tUmt havinj,' 

 been placed in the water, the density of the sample may b<! 

 read from the scale where the surface of the water touches the 

 stem. To show the sp«'cilic gravity of the water the number 

 "1.0" should always be placed before the reading taken from the 

 scale; thus, if the scale reading' is 10. the specific j;ravity would 

 be 1.010. 



The specimen of water should be taken from near the bot- 

 tom and may be conveniently obtained by lowcrinfr a corked 

 ])()ttlc or jug to the bottom and then pulling out the cork by 

 means of a string previously attached to it. After the receptacle 

 has filled it is brought rapidly to the surface without danger 

 of the sample being much changed by tlie influence of tlie upper 

 layers of the water. 



TIDES AM) CURRENT. 



The tides and currents in any region are important factors 

 in the growth and cultivation of the oyster. They bring about 

 the aeration of the water and the destruction of the dead organic 

 refuse; they have a scouring effect on the bottom and there- 

 fore clean the clutch: and at the same time are the chief means 

 for the transportation of the food materials and the young fry. 

 Stagnant water becomes exhausted in oxygen and also becomes 

 ioul from the decay of organic matter which it contains. Under 

 the influence of currents, particularly those of tidal origin, the 

 supi)ly of oxygen is renewed, and the efl'ete matter dispersed 

 ^(, that it becomes harmless. 



On densely crow-ded oyster beds the supply of food would 

 soon become exhausted unless there were some means of bi-inging 

 a fresh supply from outside sources. The oysters are inMiioval)ly 

 fixed on the beds and can take only such food as is l)rought 

 witliMi r.ach of their cilia, so that the action of the currents in 

 briii'/iiig llic food-laden water to the bed is of vital importance 

 to theii- growth. 



The genital |)roducts of both the male and female oysters are 

 simply discharged into the surrounding water. The eggs are ab- 

 solut( ly iinmotile. while the spermatozoa, or male elements, pos- 

 sess the power of locomotion to a limited extent oidy. and are in- 

 caDable of uiovinu very far dnrintr tlie short time they remain 



