EFFECT OF SEDIMENT UPUN YOUNG OYSTEES. 747 



^he cause of this was probably that the shell with its tenant had sunken too deeply into the 

 mud when the ingestion of the black ooze commenced, giving rise to the remarkable changes 

 which I have recorded. No doubt had this condition of things persisted for long the animal 

 would have been smothered by the mud. 



Mud and the young fry. — The accumulation of the slightest quantity of sediment around 

 a young Oyster would tend to impede its respiration, and in that way destroy it, yet in the natural 

 beds there are so few naturally clean places which remain so that it is really surprising that so 

 many young Oysters pass safely through the critical periods of their lives without succumbing to 

 the smothering effects of mud and sediment. When it is borne in mind that at the time the infant 

 Oyster settles down and fixes itself once and for all time to one place, from which it has no power 

 to move itself, it measures at the utmost one-eightieth of an inch, it will not be hard to under- 

 stand how easily the little creature can be smothered even by a very small pinch of dirt. The 

 animal, small as it is, must already begin to breathe just in the same way as its parents did before 

 it. Like them its gills soon grow as little filaments covered with cilia, which cause a tiny current 

 of water to pass in and out of the shell. The reader's imagination may be here allowed to esti- 

 mate the feeble strength of that little current, which is of such vital importance to the tiny Oyster, 

 and the ease/with which it may be stopped by a very slight accumulation of dirt. Mobius esti- 

 mates that each Oyster which is born has ji^sooo of ^ chance to survive and reach adult age. So 

 numerous and effective are the adverse conditions which surround the millions of eggs matured by 

 a single female that only the most trifling fraction ever develop, as illustrated by the above calcu- 

 lation. The egg of the Oyster, being exceedingly small and heavier than water, immediately falls 

 to the bottom on being set free by the parent. Should the bottom be oozy or composed of 

 sediment its chances of development are meager indeed. Irrecoverably buried, the eggs do not 

 in all probability have the chance to begin to develop at all. Tfie chances of impregnation are 

 also reduced, because the male and female Oysters empty their generative products directly into 

 the surrounding water, whereby the likelihood of the eggs meeting with the male cells becomes 

 diminished. What with falling into the mud and what with a lessened chance of becoming 

 impregnated, it is not unlikely that Mobius' estimate is very nearly correct; but the American 

 Oyster, whose yield of eggs is much greater, not only on account of its larger size, but also 

 because the eggs are smaller than those of the European, has probably still fewer chances of 

 survival. The vigorous growth of small organisms on surfaces fitted for the attachment of young 

 Oysters also tends to cause sediment to gather in such places in the interstices of tlic little 

 organic forest, where the eggs of the Oyster no doubt often become entombed or smothered by the 

 crowded growth surrounding them. 



"In addition .to the active, animate enemies of the Oyster, the beds suffer seriously, at certain 

 times, from the elements. . . . Great storms will sweep the Oysters all off the beds, bury 

 them under shifting sand or mud, or heap upon them the drifting wrack torn from the shores. 

 Beds which lie at the mouths of rivers are liable to be injured by floods also, which keep the 

 water wholly fresh, or bring down enormous quantities of silt and floating matter, which settles 

 on the beds and smothers the Oysters. 



" A few years ago a large tract of peat was drained at Grangemouth, Scotland. The loose 

 mud and moss was carried down the drains upon an oyster-bed in the estuary ; the consequence 

 was that the Oysters were covered over with mud and entirely destroyed. Nothing is so fatal to 

 Oysters as a mud storm, except it be 'a sand storm. The mud and the sand accumulate in the 

 Oyster's delicate breathing organs and suffocate him. 



" North of Long Island an enemy is found which does not exist in the milder south, in the 



