DIURNAL PERIODICITY OF PHOSPHORESCENCE. 31 
The following is a statement of the contents of the routine tow- 
nettings always taken of the plankton of the Bay, for the statistical work 
of the Biological Station, on the date (Thursday, September 24th) when 
{he second set of tow-nettings were collected for the observations :—— 
Diatoms.—Biddulphia mobiliensis, 800; Chaetoceros decuprens, 600; 
Ch. densum, 440; Coscinodiscus radiatus, 50; Streptotheca 
thamensis, 150; T'rochisca sp., 50. 
Dinornacennata, &.—Ceratium furca, 50; C. fusus, 100; C. tripos, 
100; Tentennopsis sp., 600. 
Corrrona.—Calanus helgolandicus, 50; Pseudocalanus elongatus, 3,180; 
| Lemora longecornis, 280; Centropages hamatus, 65; 
Acartia claust, 2,200; Orthona similis, 1,750; Paracalanus 
parvus, 830; Lsras clavipes, 160; Copepod nauplii, 3,960 ; 
Copepod juv., 2,180. 
Moniusca, &.—Lamelhbranch larvae, 280; Oikopleura, 3,800. 
Whether this diurnal periodicity has the same physical basis in a 
rudimentary fashion as memory in higher animals, is still an open 
question, for it is open to believe that the alternating play of light and 
darkness upon those cells which produce the phosphorescence may have 
induced in them a periodicity of activity and rest which still persists after 
the alternating stimulus is withdrawn. The process may, for example, be 
due to a secretion by certain cells which phosphoresces as each drop is 
produced, and this process of secretion may have a period of rest during 
the day and activity during the night. The rhythm of this activity may 
be timed daily under ordinary conditions, and regulated by alternation of 
heht and darkness. During the day there would be storage in the cell, 
and at night discharge. On the removal of the stimulus of hight during 
the day this state of alternation of rest and action might persist for a long 
period. 
