[11] ARTIFICIAL PROPAGATION OF OYSTERS. 751 



The remarks upon the effect of the temperature on the development 

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

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

 The range of temperature permissible with the embryo is probably 

 greater 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 

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



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

 that oysters did not exist in water of a less density than 1.01 — l.dO rep- 

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

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

 lent change of the density of the water surrounding the oysters would not 

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

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

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

 to the effect of changes of temperature. My observations during the 

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

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

 possible to eliminate the influence of either. 



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

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

 not revert to the effect upon flavor, growth, shell, characteristics, &c., 

 due* to dissimilarity in the constituents of the water ; how much or 

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

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

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

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

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

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

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

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

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

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

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

 inates. 



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

 soon has an appreciable effect upon the generative matter appears to 

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

 own opinion it is. It is well known among oystermen that transplant- 

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

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

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

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

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

 appears to be, that in the substitution of warmer water of lower specific 

 grajity, not only is the formation and exx^ulsion of the ova and sperma- 



