168 SIR W. A. HERDMAN : RESULTS OF CONTINUOUS 
March in some years, and it is not easy to determine exactly when, in the 
open sea, the fish-eggs have hatched out in quantity and the larvæ have 
absorbed their food-yolk and started feeding on diatoms. 
If, however, we take the case of one important fish, the plaice, we can get 
some data from our hatching experiments at the Port Erin Biological 
Station, which have now-been carried on for about eighteen years. We 
have records for each year of the quantities dealt with and of the dates when 
the first fertilised eggs were seen, when the various batches of eggs were 
placed in the hatching boxes, and when the larvæ were taken out to sea. 
Consequently complete series of figures for the comparison of the dates for 
fish-larvee and phytoplankton can be given for the series of years, and these 
show a certain amount of correspondence and also a certain amount of 
divergence. 
We find that the dates for the first fertilised eggs range from the middle 
of January (1920) to March 3rd (1904). Excluding these two records as 
exceptional, we have a run of 15 consecutive years with dates ranging 
from February 5th to 26th, and the average date for the first fertilised 
plaice-eggs in the Port Erin spawning pond * is about February 20th. The 
dates when the first larva are set free in the sea have varied from Feb. 23rd 
(1914 and 1920) to April 10th (1904), and the usual date is about March 20th. 
The earliest date for the phytoplankton in the sea is Feb. 5th (1907) 
and the latest April 13th (1908). Omitting February and April, we have 
a run of ten consecutive years (1910 to 1919) when the dates range from 
March 4th to 22nd, and a central date for the beginning of the diatom 
increase may be taken as about the middle of March. A central date for the 
phytoplankton maximum in these years is about the middle of May. 
It is evident, then, that in most of these years the diatoms were present 
in abundance in the sea a few days at least before the fish-larvee from the 
hatchery were set free. Out of the 13 years (L907-1919) in nine cases 
(1907, 1910-12, and 1915-19) the phytoplankton preceded the appearance 
of the larvee, and it was only in the remaining four years (1908, ‘09, 713, 
and “14) that there was apparently some risk of the larvæ finding no 
phytoplankton food, or very little, 
The evidence, so far, seems to show that if the fish-larve are set free in 
the sea as late as March 20th they are fairly sure of finding suitable food ; 
but if they are hatched as early as February they run some chance of being 
starved. 
I had an opportunity at Port Erin during the hatehing season of 1921 of 
examining the contents of the alimentary canal in a number of living larval 
and early post-larval plaice, and found :—(1) that it consisted of algal spores, 
* For further details in regard to the conditions of this experiment at Port Erin, see the 
Annual Report for 1920. 
