712 



OYSTER-BEDS, DETERIORATION OF. 



upon the temperature, the higher temperature 

 hastening and the lower retarding that event. 

 Generally, hoth in Europe and America, the 

 spawning-season may be said to be from June 

 1st until August loth, though variations of the 

 temperature and density of the surrounding 

 waters may expand or contract that period 

 considerably. 



All authorities upon the early stages of the 

 European variety concur in the statement that 

 the young oyster, or "spat," is formed by the 

 fertilization of the eggs of the female while 

 within the shell of that animal, and that the 

 " spat " is held between the gills and thus pro- 

 tected by the parent until the shell is formed. 

 Many authorities are also of the opinion that 

 the parents are hermaphrodites ; but the accu- 

 racy of this view is open to much doubt. The 

 most material difference between the Euro- 

 pean and American varieties is in the manner 

 of impregnating the eggs of the female. Ac- 

 cording to the best authorities, the eggs of the 

 European variety are fertilized by the passage 

 of the male fluid into the water, and thence 

 between the valves and gills of the female. 

 The young resulting from the union of the ova 

 and spermatozoa are held and protected within 

 the gills of the female until the shells are 

 formed, and until they are quite well advanced 

 in development, having at the time of their 

 expulsion locomotive powers of their own, 

 which enable them to swim about and seek a 

 fit place for attachment. 



The American variety differs in this, that 

 the young oyster is not found within the gills 

 of either parent, nor does the fertilization take 

 place within the shell, but the contents of the 

 generative organs of both sexes are expelled 

 into the water, there to stand the chance of 

 coming into contact. It is evident that a large 

 measure of protection is afforded the young of 

 the European variety by the inclosing shells of 

 the parent, and that this protection is given 

 during the most precarious stages of their ex- 

 istence, while the ova and spermatozoa of the 

 American oyster are not only left to a happy 

 chance for their successful union, but the re- 

 sulting young are exposed, unprotected, to all 

 the vicissitudes of climate, and to the ravages 

 of all enemies. 



After the formation of the shell and the de- 

 velopment of the locomotive powers, the young 

 of both varieties begin their search for a per- 

 manent resting-place or point of attachment. 

 Such points of attachment must soon be ob- 

 tained, or the young oyster perishes. Any 

 moderately rough, hard substance, provided 

 the surface is clean, is suitable for the purpose, 

 and such objects, placed so as to attract the 

 young brood, are called "cultch." Pieces of 

 wood, planks, stones, old shells, tiles, etc., have 

 been successfully used. Upon finding the 

 "cultch," the "spat" attaches itself firmly, 

 and thenceforward, so far as its own power is 

 concerned, is located for ever. 



The development is now one of ordinary 



growth, the animal having passed through its 

 embryonic life; its organs are formed and in 

 active operation ; it is but immature. The 

 American variety increases more rapidly than 

 the European. Observations during the sum- 

 mer of 1871) in Chesapeake Bay show that, in 

 the first three months of existence, the oyster 

 increases in size from a hardly visible speck to 

 an average length of one and a quarter inch, and 

 a few were over two inches long. After the first 

 year the increase is not so rapid, and oysters 

 of two or three years of age are about two 

 inches broad and three inches long. In three 

 years, at the most, the American oyster is con- 

 sidered mature. With the European variety 

 the growth is much slower, and at maturity 

 they are very much smaller than the American 

 oyster. 



"With all animals Nature strives to provide 

 against the destruction of the young alter birth 

 by insuring a sufficient number to allow for all 

 ravages ; and the greater the danger to the im- 

 mature the larger will be the number provided 

 to meet those dangers. Hence, as the embryo 

 European oyster receives some protection and 

 the American none, it is inferred that the 

 number of American embryos in any commu- 

 nity will be subjected to greater danger, and 

 consequently it is probable that a larger num- 

 ber of eggs and spermatozoa are provided, that 

 the production may not be less. Investigations 

 seem to support this conclusion. Professor 

 Mobius, in his work on the oyster and oyster- 

 culture, estimates the number of eggs spawned 

 by the European variety as nearly 2,000,000, 

 and his estimate is supported by Eyton, in his 

 "History of the Oyster and Oyster Fisheries." 

 Professor Brooks estimates the possible num- 

 ber of eggs spawned by the American variety 

 to be as large as 00,000,000, and the average 

 number to be over 9,000,000, or about nine 

 times as many as the European variety spawns. 

 The number of embryos surviving and matur- 

 ing can not be accurately stated for either va- 

 riety, as we have not data sufficient to deter- 

 mine the question. The results, however, of 

 Professor Mobius's examinations of the Schles- 

 wig-IIolstein beds are valuable and suggestive. 

 These were made by government officials from 

 1730 to 1852, in 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 styled marketable, 

 medium, and young growth. The first were 

 the full growth and mature, from two and 

 three quarters to three and a half inches in 

 length and breadth, and about seven tenths 

 of an inch thick. The medium oysters were 

 those half grown, from six to seven tenths of 

 an inch thick, and about three inches in 

 breadth. The young growth were those of 

 one or two years old. 



From these observations, made annually, 

 Professor Mobius discovered that there were 

 on an average 421 medium oysters to every 



