11] ARTIFICIAL PROPAGATION OF OYSTERS. 751 



The remarks upon the effect of the.teraperature on the development 

 If the egg hold good, to some extent, with regard to the development 

 If the embryo, though I did not make any experiments upon the latter, 

 the range of temperature permissible with the embryo is probably 

 rreater than with the egg. At least I noticed that a sudden fall of tem- 

 perature which would destroy the eggs did not apparently have any 

 fleet upon the swimming embryos, certainly not any immediate one. 



Density. — Some years ago Count Pourtales called attention to the fact 

 jjhat oysters did not exist in water of a less density than 1.01 — 1.<10 rep- 

 jesenting (he density of distilled water. My investigations in the Ches- 

 jpeake lead me to the same conclusion, and I also inferred that a vio- 

 3nt change of the density of the water surrounding the oysters would not 

 inly affect the mature animals, but would influence the formation of 

 (he generative fluids, their development, and the different processes by 

 7hich they were converted into " spat," in a manner somewhat similar 



the effect of changes of temperature. My observations during the 

 fiast season tend to confirm these latter impressions, but the changes of 

 iensity and temperature are usually so closely correlated that it is hardly 

 jitosslble to eliminate the influence of either. 



1 As I am not here dealing with the mature animal, except so far as is 

 lecessary in considering the artificial production of the young, I shall 

 iiot revert to the effect upon flavor, growth, shell, characteristics, &c., 

 .ue to dissimilarity in the constituents of the water; how much or 

 little they influence reproduction, it is, in the absence more exhaustive 

 xperiments, at present impossible to say; but the following points are 

 If interest : Shoal-water oysters spawn first, and the less the depth of 

 /ater the less the density. Also, shoal- water oysters generally lie in 

 he neighborhood of fresh-water streams, or in water of low specific 

 jkravity. Deep-water oysters, or those exposed to exactly opposite con- 

 jiiitions, not only present exactly opposite characteristics to the shoal- 

 rater oysters as regards time of spawning, but they also, so far as my 



observation extends, contain a much smaller amount of generative mat- 

 er. So many other conditions obviously operate in effecting the fore- 

 'oing that it is, however, impossible to decide which influence predom- 

 ;flate8. 



That a change from water of considerable density to that of less very 

 oon has an appreciable effect upon the generative matter appears to 

 Jpe settled ; that the effect is a deleterious one is not so clear, but in my 

 I'Wn opinion it is. It is well known among oystermen that transplant- 

 Qg during the spawning season puts a stop to the reproductive process; 

 fr as they express it in the Chesapeake region, " Plants do not spawn " 

 uhe transplanting there is from deep and dense water to shoal and 

 ffackish, and my own experience at Fair Haven under similar condi- 

 ,jiions leads me to conclude that the oystermen are correct. The cause 

 ll-ppears to be, that in the substitution of warmer water of lower specific 

 jCraTity, not only is the formation and expulsion of the ova and sperma- 



