142 
appeared that merely sufficient to go 30 or 40 times a day over 
the eggs was employed during the whole of the time of incu- 
bation. On December 21st, I gave Mr Ogden about 200 of 
these eggs, which he took to Matlock, where they were placed 
in trays supplied with a good stream of water, and here they 
hatched more than a month prior to the remainder which had 
been kept at Cheltenham. It would here seem most probable 
that a slow stream is equivalent to diminished supply of oxygen 
to the embryo, and which may be one reason of lengthened 
incubation. 
The character of the water employed may be inimical to 
the embryo during incubation, or to the young when hatched ; 
while impurities may be natural or acquired, and can be thus 
summarised. Poisoning due to the character of the water itself, 
either directly by vegetable substances as by their decomposi- 
tion—or chemical ingredients as from the refuse of mines or 
factories—or by mechanical causes as occasioning suffocation 
by mud or sediment present in the water. In fact ova may be 
deleteriously affected by water which is not obtained from a 
clear and wholesome running stream; while on the contrary 
should it be distilled they become suffocated, owing to the 
absence of air in solution. If it is muddy they are likewise 
suffocated from the sediment covering the porous egg-shells, 
whereas water taken from pumps, or wells, or collected from 
rain will answer, provided no other deleterious ingredients 
are present. But for young fish the two first descriptions (bad 
or distilled) of water will be equally fatal, as they are to the 
eggs, and so also will that taken from pumps, wells, or rain 
unless suitable food be added. 
One of the forms of pollution to which I turned my atten- 
tion was the action of paraffin, for in a former paper I sug- 
gested that I had traced it as having injuriously affected some 
grayling eggs* consequent upon my having employed an 
insufficiently deodorised cask as a reservoir for water. This 
product of wood-oil when chemically pure is doubtless insoluble 
* Grayling eggs and young require purer water than such as will succeed 
with trout. 
