s a, m. pic 
68 
J. M. Thomson. 
It will be noticed that two crops of TJlva lactuca occur during* the year. 
Cystophyllum muricatum was not collected in August, and in September 
01? lv a small specimen was found, after which none occurred. The dates of 
appearance and disappearance of other algae can be seen from the graph. . 
A tremendous increase in animal population is indicated in November. It 
can be seen from the graph that the summer population is several times 
greater than that in mid-winter. 
IWQ 
Text fig 1 : Variation in population density. March-December, 1943. 
