14:2 
mated “marketable,” “medium” and “young growth.” The* 
“marketable” oysters were full grown and mature, from 
seven to nine centimeters in length and breadth, and eighteen 
millimeters thick. The “ medium ” were half grown oysters, 
from sixteen to eighteen millimeters thick, and of less than 
nine centimeters in breadth. The “ young growth ” were those 
one or two years old. From these observations Prof. Mobius 
discovers that there was an average of 421 medium oys- 
ters to one thousand full grown ones ; that is, out of every 
1421 oysters there would be only one thousand full grown 
ones. (?) The average of all observations differ very little 
from the number given by each, and consequently shows that 
there was but slight fluctuation in the proportion in 122 years. 
The medium oysters are considered by Prof. Mobius to be 
those descendants of the marketable ones that have survived 
their most precarious years of existence, and escaped their 
principal enemies, and are consequently likely to reach their 
full growth. They thus represent the total number of em- 
bryos spawned which have survived in the struggle for ex- 
istence. From his (Mbbius’) experiments, he decides that an 
oyster spawns about one million embryos in a season, and that 
forty-four per cent, of the mature oysters give forth “spat.” 
[Other authorities are of the opinion that only about ten per 
cent, spawn ; Prof. Mobius’ data appears hardly sufficient to 
justify his conclusion.] 
From the above it is evident that in an assemblage of a 
thousand oysters, 440,000,000 embryos can be voided every 
season, and of them 421 would survive, or 1,045,000 embryos 
would be destroyed where one was preserved. But the me- 
dium sized oysters also, spawn, though they send forth a much 
smaller number of embryos. Mobius estimates that the 421 
in the community w T ould produce about 60,000,000 of “spat.” 
It would therefore require about 500,000,000 embryos to pro- 
duce 421 medium oysters, or 1,185,000 to produce one. From 
the above it is evident that it would be necessary to have 4.2 
oysters assembled to produce one, though the proportion would 
only hold where there are much larger assemblages. Regard- 
ing these results, Prof. Mobius is of the opinion that no more 
