[13] EXPERIMENTS IN OYSTER CULTURE RYDER. 775 



I examined some very minute fry and spat obtained from old oysters 

 touged up in the deeper waters some distance oft* shore to-day. I re- 

 moved them from their attachments as carefnlly as I could and placed the 

 living translucid spat, measuring from a sixteenth to an eighth of an 

 inch in diameter, under a compressor for more critical examination un- 

 der the microscope. I counted the heart beats by my watch in these 

 young oysters, the cardiac contractions being visible through the shell. 

 The her.rt I found to pulsate at the rate of eight to twelve times per 

 minute, and appeared to be somewhat irregular in its action. 



August 2. — Examining the embryos placed In the closed circuit and 

 aquarium yesterday, 1 find that they are for the most part dead, even 

 under the most favorable conditions. The temperature in the closed 

 circuit or McDonald apparatus with the cooling attachment remains 

 quite constant and stands at about what it did at first. Not yet content 

 with my results I fertilized another Ipt of eggs at 3 p. m. to-day. 



August 3. — I fertilized another lot of eggs to-day at 12 m. The lot of 

 the previous day appear to be dead ; cannot find any alive in the appa- 

 ratus. 



August 4. — Eggs and embryos of yesterday have disappeared. The 

 dead embryos and unimpregnated eggs appear to have become the prey 

 of large numbers of Actinophrys sol, a sun animalcule, which has multi- 

 plied rapidly in the closed circuit and aquaria. I find in fact some of 

 these animalcules embracing and enveloping dead oyster eggs, which 

 they appear to grasp and surround bodily with their own living sarcode. 

 They aj^pear to me to be really scavengers, and not at all destructive 

 to living oyster embryos which have begun to swim. In fact the 

 Actinophrys ca mot pursue its prey, being very slow in its movements, 

 and progresses with a very deliberate rolling motion; not swift enough 

 to follow a healthy young oyster provided with a well developed velum. 



August 5. — The density of the water in St. Jerome's Creek ranges from 

 1.007 to 1.0095 according to the standard hydrometers used by the United 

 States Coast Survey. At the beach opposite the barges the density 

 was found to be 1.01 and a quarter of a mile off shore it was found to be 

 about the same. For the determination of the density off shore I am 

 indebted to the kindness of Dr. J. Alban Kite, of the steamer Fish Hawk. 

 The specific gravities indicated above are greatly below the average of 

 the ocean, as appears upon comparison with a table given by Young, in 

 his Physical Geography, where it is stated that the specific gravity of 

 the water Of the ocean ranges from 1.02548 to 1.02919. The waters of 

 the Chesapeake do not appear to have a density much above that of the 

 Black Sea, even near their confluence with the Atlantic at Hampton 

 Eoads, where the specific gravity is 1.014. As one recedes from the 

 mouth of the bay to the north the density diminishes, so that over a 

 large part of its area it is practically little more than brackish. Along 

 shore and in the estuarine ]iroIongations of the bay inland is where the 

 oyster of the Chesapeake is at home. From their prolonged stay gene 

 ration after generation in water of approximately the same si)ecific 



