510 TRANSACTIONS OF SECTION D. 
factor explains certain apparent irregularities in the daily rhythm not described 
above, more particularly the behaviour of the organism during the night, upon 
which observations have also been made. Temperature does not appear im- 
portant in the present connection. 
(b) A lunar periodicity. Amphidinium lives not far below the high-water 
mark of spring tides, so that the neap tides do not reach it. A periodic 
alternation of ‘spring’ periods of activity and ‘neap’ periods of comparative 
inactivity is associated with the amount of water in the sand. 
(c) An annual periodicity. There has been a considerable change in the 
appearance of the Amphidinium area as the year has advanced, apart from the 
changes recorded above. There was a strongly marked maximum from 
February to end of April, at which latter time the area reached its greatest 
size, being 40 yards across and extending along 220 yards of coast line, the whole 
composed of practically continuous smaller patches, appearing as a brown-green 
carpet on the shore, and very clearly visible a hundred yards away; during 
May the number began to decrease, the decrease became very marked during 
June, and they have not been seen on the surface of the sand since the first 
week in July, though up to the end of July a few are still to be found in samples 
of sand examined under the microscope. It is interesting to note that during 
the latter half of June numerous dead examples were found in the sand, which 
in dry warm weather had not been covered by the tide for several days. 
Large elongated form. On July 6 a small patch about 6 inches square of 
a more yellowish tinge was noticed on the lower and damper margin of the 
area. It was composed of the larger, more elongated form found at Port 
Erin last autumn, another small patch appeared 30 yards away two days 
later, and two days later again numerous small patches were to be seen con- 
tinuing up to the present time, gradually spreading seaward so as to cover a 
larger area which, however, is still small as compared with that occupied earlier 
in the year by the more rounded form. At present it appears each day at about 
6.0 p.m. The whole area is well above the high-water mark of neap tides. 
This larger form replaced the smaller at Port Erin in autumn 1912, also two 
forms, which may be the two under consideration, were, I understand, found 
at Cullercoats by Meek this summer, and as Daniel and Hamilton have just 
found both forms on the West Coast of Ireland and Herdman on the Island of 
Iona it appears quite possible that they may be phases of the life cycle of the 
same organism. There is as yet no direct evidence of this. I am inclined to 
believe that the balance of what evidence there is points to their being different 
species. 
The methods of migration of A. operculatum are elusive. It has not been 
found in any of the large numbers of tow-nettings taken by Professor Herdman, 
appearing to be essentially a sand dwelling form. I have kept cultures for a 
month in water without sand and found the water full of freely swimming 
organisms throughout this period, so that migration across seas is evidently 
quite feasible, and it is not necessary to its existence that it should live always 
between the tide marks. 
The optimum light intensity for Amphidinium is not the same as for Con- 
voluta, or for certain diatoms which I have observed at Hoylake and Port 
Erin, or as for euglinoids which I have watched at Port Erin, so that the 
periodic movements of these various organisms on the shore differ from each 
other in characteristic ways. 
The bulk of the observations have been made at Hoylake, but I examined 
the rounded form at Port Erin during the first three weeks in April for pur- 
poses of comparison. At Port Erin Amphidinium lives a little lower on the 
shore than at Hoylake, so that it is covered even by neap tides. This is likely 
to involve well defined differences between its scheme of periodic movements 
and that of the Hoylake race. 
N.B.—The colour of A. operculatum is due, as in crude chlorophyll, to two 
pigment groups. On shaking in an alcoholic extract with benzine these separate ; 
one of them, more soluble in the benzine, is green and gives an absorption 
spectrum which falls within the limits of variation of the spectrum of the 
blue-green element in chlorophyll, while the other, which remains in the alcohol, 
has in an exaggerated condition the broad absorption band of the Xanthophyll 
type at the blue end of the spectrum. 
