[45] THE OYSTER AND OYSTER-CULTURE. ae 
of swine and other animals, and after the Dutch, still later, had ruth- 
lessly killed many of these birds. Also, at present, there are no turtles 
at Mauritius, while up to the year 1740, according to written testimony, 
hundreds were caught there for the provisioning of ships. Certainly 
many young dodos and turtles must have been devoured by the pigs. 
The beaver (Castor fiber) will perhaps very soon have vanished from our 
biocénotic transformed portion of the earth. The Greenland whale 
(Balena mysticetus) is now seldom seen in the neighborhood of Spitzber- 
gen and Greenland, on account of the persecution to which it has been 
subjected since the seventeenth century. Every biocénotic territory has, 
during each period of generation, the highest measure of life which can 
be produced and maintained there. All the organic material which is 
there ready to be assimilated will be entirely used up by the beings 
which are procreated in each such territory. Hence at no place which 
is capable of maintaining life is there still left any organizable material 
for spontaneous generation. If, in a biocénose the number of individ- 
uals which arrive at maturity would be maintained at the highest point, 
even though the number of breeding individuals is being artificially 
lessened, the natural causes which act towards the destruction of the 
embryos must be diminished at the same time. In the Bay of Arcachon 
the breeders raise to maturity an unusually large number of young oys- 
ters by guarding them artificially from their enemies. 
In an example in subtraction the remainder may be kept unchanged, 
or even increased, if the subtrahend is decreased at the same time as the 
minuend; and the mass of individuals of any species may be increased 
permanently if the biocénotic territory is extended. Thus, when the 
Lim Fiord became filled with water from the North Sea, the number of 
mature oysters over the territory of the North Sea coast of Denmark in- 
creased to more than seven millions (chapter 8, p. 30). The oyster-beds 
in the Bay of Arcachon and the claires, or fattening-ponds, at the mouth 
of the river Seudre (p. 27), are artificial extensions of oyster-territory. 
The individual number of cultivated plants and animals has been im- 
‘mensely increased because man has artificially extended their biocénotic 
territory; and this artificial increase in the number of plants and ani- 
mals by means of cultivation is the foundation for the increased fecundity 
of the human species and the greater number of individuals which 
arrive at maturity—that is, for the extension of the biocénotie territory 
of Homo sapiens. The average yieid of our woods, fields, and gardens 
is the result of natural force and human labor, for in addition to the 
chemical and physical forces of earth and air, and the organic forces of 
wild and cultivated plants and animals, the bodily and mental forces of 
man play an important role in the culture of field and forest, and a very 
significant share of the large yields of harvests is due not only to the 
numerous workmen of the woods and fields, but also to the makers of 
implements of labor, to the mechanics and opticians who produce in- 
struments for the investigation of natural phenomena, and to the care- 
