EFFECT OF HEAT VTON OYSTERS. 743 



shells taken from the shores of England and placed in the Mediterranean at once altered their 

 manner of growth and formed prominent diverging rays, like those on the shells of the proper 

 Mediterranean Oyster. The same individual shell, showing both forms of growth, was exhibited 

 before a society in Pafis." 



Variations m the shell. — The statement by Mr. Buckland in regard to the local forms of 

 Vstrea edulis is undoubtedly true, as I know from personal observation of specimens oi-tained for 

 me from various parts of Europe through the efforts of Professor Baird. In some cases the local 

 •differences between the shells from different places were so marked that had a person mixed certain 

 lots together indiscriminately without my knowledge I could afterwards certainly have sorted out 

 the more marked varieties. Local influences also very largely determine the " greening" of Oysters, 

 as I can assert from personal observation of both the American and European species. Practical 

 •oystermen afiSrm that they can readily discriminate the local varieties of Oysters grown in various 

 noted localities along the eastern coast of the United States. From what I have seen it is very 

 ■probable that this may be the case, as one may often observe well-marked differences of form as 

 "well as color. 



Local adaptation undoubtedly takes place, for how else are we to account for the fact that 

 a change in the specific gravity of the water to which the adult has been accustomed will kill the 

 milt? This point has an important practical bearing in relation to the effect of heavy rains in 

 •diluting the water when the animals are spawning. Might not a marked change in the specific 

 gravity of the water at the time of spawning kill all the spermatozoa which are set free, and thus 

 •also prevent the impregnation of whatever mature ova were being thrown out at that time by 

 the adults'? 



Influence of tempeuatuke. — Certain It is that temperature has an influence upon the 

 time of spawning. A lot of Oysters marked "Anglo-Portuguese," which had been transplanted 

 from Portuguese to English waters, and which I received in the month of March and others 

 in January last, had the reproductive organs remarkably advanced in development as compared 

 -with specimens of 0. edulis from different parts of England, Wales, Scotland, Holland, and France. 

 ^0 great was this difference that, although planted for some time in the colder waters of England, 

 the reproductive organs of the Portuguese form had not apparently had their disposition to 

 become fnnctiolially active at this early season influenced to any great extent. In fact, I obtained 

 living mature eggs and milt from a number of specimens of this variety, while I looked in vain 

 for ripe spawn in any of the others of the true 0. edulis. This would indicate that thfe influence ot 

 temperature, though not altogether hereditary in this case, was persistent, and had so impressed 

 itself that the reproductive organs of these Oysters,,co.ming from a warmer latitude, had begun 

 to mature their sexual products even after transplanting into more northerly and colder waters 

 much sooner than the natives of those same latitudes. 



Like this persistent influence of a climate to which certain fdrms of Oysters have been long 

 -accustomed, the influence of the specific gravity of the water of a certain locality may also be 

 persistent; The Oysters of Saint Jerome's Creek seem to be adapted Jo the specific gravity of 

 the water of the vicinity, so that if artificial sea- water is ijrepared, differing much in this regard 

 from the native water, we find that the spermatozoa are immediately killed if put into it. From 

 this it follows that if the specific gravity to which the adults become accustomed is normal to 

 their sexual products, may it not be well to look into the effect of such changes upon the health 

 ■of the adults ? 



I have met with spawning Oysters in December, such at least in which the spawn was neairly 

 mature, but this was an exceptional case. I find them in April and May in considerable abun- 



