776 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [14J 



gravity they have become adapted to it, as would appear by the facts 

 to be cited in the sequel. 



I impreguated two lots of eggs in water of specific gravity 1.009, and 

 in water of specific gravity 1.021 respectively, the latter having been 

 prepared artificially^ from fresh water to which sea salt had been added. 

 This experiment showed us that the Saint Jeromes oysters could not 

 be impregnated in water as dense as the last mentioned. The milt was 

 killed by increasing the specific gravity even to a comparatively mod- 

 erate degree. The eggs sank in water of the greater as well as lesser 

 specific gravity. The spermatozoa became immobile in the denser water 

 almost immediately, or in that which was abnormal to them. This ex- 

 periment was repeated, in order to verify my conclusions, with the same 

 result as before. A specific gravity of 1.013 was the limit of change 

 which appeared to be endurable by the spermatozoa. These are singu- 

 lar facts, and show how nicely the vital conditions of the oyster have 

 been gradually adapted to the environment. These facts appear to in- 

 dicate that the characters of the protoj^lasm of a species themselves 

 become specific in consequence of such adaptations. 



The embryos of day before yesterday I find to be dead. Both lots of 

 to-days' eggs poor; spawn is apparently getting scarce. Myriads of 

 spat, I find, have caught on the shells in the natural beds out in the 

 bay off the barges. This young spat measures from ^ millimeter up to 

 a quarter of an inch in diameter. It must have caught for the most 

 part within the last two weeks. 



August 6. — I found young oysters to-day on the shells of the old ones 

 measuring only one-ninetieth of an inch in their shortest diameter. 

 This is about the size which was asserted by me to be the limit of the 

 dimensions of the fry two years ago.* The shell of the spat develops 

 continuously from the rim of that of the fry, but presents a totally dif- 

 ferent microscopic character. Both dissolve readily in acetic acid under 

 the microscope, leaving the organic matrix of conch ioline behind. The 

 fry shell has well-marked lines of growth like that of the spat, but 

 homogeneously transparent, and, unlike the shell of the sjiat, does not 

 have its carbonate of lime arranged prismatically in an organic matrix. 

 It looks like a Pisidium when viewed from the side, and like a Cardium 

 when looked at from the end, being very ventricose and i)erfectly sym- 

 metrical. After decalcification with acid the line of demarcation be- 

 tween the spat shell and that of the fry remains indistinctly marked in 

 the matrix. The horny membranous matrix afterwards dissolves very 

 .slowly in caustic i)otash. It has been very hot to-day, the air being 

 93° Fahr. in the shade. The temperature of both air and water are 



* See first, series of these iuvestigatious, in Appendix A, to Report of T. B. Fergu- 

 son, A Commissioner of Fisheries of Maryland, rfagerstowu, 1881, pp. 59, figures 6 and 

 7, in Report entitled "An account of experiments in oj'ster culture and observations 

 relating thereto, made at Saint Jerome's Creek, Maryland, during the summer of 1880," 

 by John A. Ryder. 



