284 
Proceedings of the Royal Society of Edinburgh. [Sess. 
in the bottom and leave them to climb out ; this they did, passing the edge 
and falling on the floor. Latterly a large number were placed in the jar 
one day and next day those on the side of the jar counted. It seems 
evident that we are dealing with the tail of a moving mass, and that this 
tail should obey the law of the exponential. In one experiment the number 
of Littorina in each half inch of the jar, measuring from the top, were as 
shown in table on page 283. 
X 
This gives a distribution y = 2'12e~^^' 
As it stands = 10'2, so that P = '53, but, as before with Daphnia, 40 per 
cent, of the value of is accounted for by the third last group. If this be 
subtracted P = *87. In either case the fit is admissible. 
Z? 
L/TTOR/Nfl 
\ 
20 
\ 
\ 
\ 
/5 
\ 
/ Q 
v; 
S 
V* 
-•A" _ 
Other Marine Animals. 
With regard to large animals few experiments can be recorded. Some 
observations were made on fish. In fish migration the form of the shoal 
should be capable of measurement. In this case the tanks in the Millport 
Biological Station seemed to afford some chance of success. One of the 
large tanks contained a small shoal of saithe ( Gadus virens). These were 
photographed several times, but to get sufficient light for an instantaneous 
plate was difficult. In one such photograph the shoal is on the point of 
turning. The symmetry is remarkable, the numbers from the left to the 
right in each unit of length being as follows : — 
1, 2, 2'5, 6, 6, 2-5, 1, 1. Total 22. 
The numbers are too small to allow of differentiation of the type of curve, 
as they can be fitted either to the exponential curve described or to the 
normal curve of error. 
