414 F. W. GAMBLE AND FllEDERIOK KEEBLK. 



tide falls, the patches of Convoluta make their appearance 

 and rapidly increase to a maximum size, which maintains 

 itself for several hours and then falls off steadily till the 

 tide turns ; and so on day by day. From this it will be 

 clear that each Convoluta submits itself to a certain spell 

 of insolation, after which it withdraws from the surface, 

 leaving others, which meanwhile have been shaded by it, to 

 take its place and retire in turn. 



The tidal periodicity which we have recorded in our 

 experiments (Sect. IV, 3, p. 401) manifests itself as a practice 

 steadily recurring in nature. 



Lunar Period Variation. — The size of the component 

 patches of a colony undergo a variation, which has a relation 

 to the alternation of spring and neap tides. The text-fig, 5 

 shows the nature of this variation. As the neap tides 

 give rise to the spring tides, the patches increase to a 

 maximum, only to fall off again during the ensuing week. 

 The extremes of this variation are shown on PI. 30, figs. 1, 2, 

 and its course for August and September, 1902, are shown 

 on the accompanying text-figure. 



The explanation of this variation is probably to be sought 

 in phenomena of reproduction and of growth. The older 

 individuals of a colony are almost invariably in the same 

 phase of growth. Those of a fertile colony become mature 

 simultaneously, and lay their eggs about the same time. 

 This time coincides with the onset of the spring 

 tides. During the antecedent neap tides the animals about 

 to engage in oviposition apparently remain below the surface^ 

 where, indeed, the eggs are laid. 



4. General Phenomena of Reproduction and 

 Development. 



During the summer, certain patches of Convoluta remain 

 for months in an immature condition, whereas neighbouring 

 patches pass through a series of mature, alternating with 

 immature, phases. Large numbers of members of these 



