46 



case, owing to the increased amount of "cultch" due to the fishing of the beds, and aside from 

 thai the conditions surrounding and operating upon the beds are so similar to those in the pasj 

 that the loss of the young could not be much greater from the want of attachment. 



The freshets and other natural causes for diminished numbers of young have also been long- 

 in operation and the deterioration cannot be justly assigned to them. Remaining then to be 

 accounted for are the ravages of enemies. Those found by us during the season were astyris in large 

 numbers, a few welks, and a very few starfish, but as the oystermen were ignorant of both their 

 presence and destructive effects I am unable to decide whether they have increased or diminished 

 in numbers. There is no doubt that very large numbers of young are destroyed by the drills or 

 welks; fully fifty percent, on some beds in Pocomoke Sound, and if these small enemies have 

 only within late years entered the Sounds we have one of the principal causes for the deterioration 

 of the beds. But as there is also a marked deterioration upon those beds upon which no drills 

 were found, still another cause must be at work and must be sought in the non-production of the 

 young. 



This is caused by the failure of the "brood" oysters, they having been removed or become 

 extinct, thus causing a failure of impregnation. If the theory is correct that there is a mutual 

 fecundation, partaken of by all oysters on the beds, the spermatozoa being formed and milted 

 somewhat prior to the formation of ova, then it can easily be understood that if the oysters are 

 so much separated that even the tides and currents cannot bring the spermatozoa within reach 

 of the adjacent animals, there could be no production of young. Taking for instance the most 

 exaggerated case in both Sounds, that of the Muddy Marsh Bed, it will be seen that the set of the 

 current over it is not generally from any other adjacent bed, the nearest one being Parker's Rock, 

 which is over .'5 miles distant; the oysters on the Muddy Marsh Bed were very few, and the mass 

 of shells immense, affording ample surface for the attachment of the drifting "spat," should there 

 be any. But supposing the oysters on the beds to have been so much diminished that they were 

 not sufficient for mutual fecundation, the distance aud situation of other beds is such as to prevent 

 the current from bringing the products of generation voided on them to the Muddy Marsh rocks, 

 and there would be, as was noticed, an almost entire failure of young. In the same, though less 

 degree, would the other beds suffer, the amount ot spawn voided depending not only upon the 

 number of mature "brood " oysters, but upon their distance from each other and the spaces sepa- 

 rating the beds. This theory is supported by the investigations that have been made in England, 

 France, and Prussia, and almost all opinions coincide that the number of young iu any spatting 

 season is dependent upon the number of "brood" oysters upon the beds. Indeed, it seems so 

 self evident a proposition that it is hardly worth while to experimentally establish it. It is neces- 

 sary, then, having accepted the theory, to determine what proportion of the oysters should be 

 taken off' the beds, and what proportion is actually removed. As there is uo data to my knowl- 

 edge derived from observations made in this country to determine the first of these two desired 

 points, it is necessary to turn to the, experience of foreign oyster fisheries for guidance, and though 

 the animals and the conditions under which they live are not entirely similar, yet some information 

 may be obtained and a line of investigation marked out for the future. 



The following is a synopsis of the deductions of Professor Karl M obi us, professor of zoology in 

 the University of Kiel, whose work, in manuscript, ou the oyster was kindly lent me by Professor 

 Baird. The observations were made over the Schleswig- Uolsteiu oyster beds by government officials 

 from 1730 to 1852, and were carried on in, practically, the following manner: Each bed was dredged 

 over in three or six places, according to its size, and the oysters taken were divided into three 

 classes and carefully counted. The classes were denominated " marketable," " medium," and "young 

 growth." The "marketable" oysters were full grown and mature, from 7 to 9 centimeters in length 

 and breadth, and 18 millimeters thick. The '•medium" were half-grown oysters, from 10 to 18 mil- 

 limeters thick and of less than 9 centimeters in * readtb. The "young growth" were those one or 

 two years old. From these observations Professor Mobius discovers that there was an average of 

 421 medium oysters to 1,000 full grown ones. The average of all the observations differs very 

 little from the number given by each, and consequently shows that there was but slight fluctuation 

 in the proportion in one hundred and twenty-two years. The medium oysters are considered by 

 Professor Mobius to be those descendants of the marketable ones that have survived their most 



