THE ALCYONARIA OF THE MALDIVES. 475 



Conversely, we may argue that if the colour and mode of branching are of little importance 

 in the struggle for existence of the species the offspring of a single pair of parents will 

 probably show a great range of variation in these characters, BD x BD gi"ving rise to 

 BD's, R(Ts, YF's, etc. in varying proportions. 



It is impossible to believe that the struggle for existence has much influence upon 

 the colour of these Alcyonarians. There is no evidence that the colours can be of assist- 

 ance to the species either as apatetic colours, hiding the individuals from their enemies by 

 resembling the suiToundings or some other dangerous zoophyte, or as aposematic colours, 

 signalising some dangerous sting or abhorrent taste. 



Spongodes are, so far as my experience goes, extremely conspicuous in their proper 

 surroundings, and do not mimic any other zoophyte that is usually associated with them 

 on the same reef. If they were of the nature of warning colours we should expect to 

 find them on the Miillerian principle of one or two distinct kinds, and arranged in simple 

 patterns instead of the endless shades of tone and tint and kaleidoscopic arrangement that 

 they exhibit. It is difficult to suggest any use that these colours can be to the Alcyonarian, 

 and they should be regarded as being of a purely physical and chemical character, as the 

 green of chlorophyll and the red of haemoglobin, and having no biological significance. 



The exact form and mode of branching of tiie colonies must in m}' opinion depend 

 very largely upon the external conditions of the individuals. Just as a tree or shrub will 

 vaiy in form according to its exposure to the wind, the character of the soil, and the proximity 

 of other shrubs and trees, so will a Spongodes vary in form according to the strength of the 

 tides flowing over it, the amount of food these tides bring, the proximity to other zoophytes, 

 the exposure to sunlight, and other external conditions. The external conditions that may 

 influence the growth of a Spongodes are so many that it is not surprising that we find 

 so many differences in the style of ramification. One specimen may be free to expand in 

 any direction and receive the full benefit of all the sun's rays that penetrate to the depth 

 of water in which it lives, whereas another not a foot away may be impeded in one 

 direction or another by the branches of a great Madrepore and sheltered from the heat 

 and light of the sun by the shadows which the gi-eat coral casts. It appears to me there- 

 fore far more probable that the critical condition of life for a Spongodes is not that it 

 should branch in any one pattern that is inherited from its parents, but that it should 

 be able to adapt itself to any one combination of the great variety of conditions which 

 it may happen to meet in the course of its development. Apart from the purely physical 

 conditions determining the shape of a colony, there is one biological condition which is 

 probably of veiy great importance. It is well known to those who have handled museum 

 specimens of Spongodes and many other Alcyonarians that Crustacea of various kinds are 

 frequently found entangled in the branches; and Mr Gardiner has called my attention in 

 his manuscript notes to these Crustacea and the striking similarity of their colours to the 

 colours of their host. It is very probable that these Crustacea render an important service 

 to the Spongodes in keeping their surfaces free from the larvae of Sponges, Barnacles, 

 sedentary worms and other animals, and it is also probable that the character of the 

 ultimate ramifications is due in no small measure to the size and shape of these important 

 epizoites. The manner in which the epizoic crabs affect the growth of Pocillopora, Seria- 

 topora, and other corals, and form galls, is well known. There is some reason to believe, as 

 stated on p. 49-5, that the tubes of Solenoccmlon are caused by the Alpheids which infest 



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