4 
water. Déstichopora is confined to shallow water. The genera Errina, Cryptohelia and Conopora 
are confined to deep or very deep water, (204—1633 metres). 
The genus Déstchopora is undoubtedly very common in the shallow waters of the Malay 
Archipelago and is probably represented by only one variable species’). Only one specimen 
however was included in the collection sent to us and this presented no features of special interest. 
The genus Stydaster however is represented by a large number of specimens from depths 
ranging from O—1633 metres, and it is in this genus that we have found the greatest difficulty 
in assigning specific names to the specimens. 
Stylaster is one of those genera of zoophytes which, like J/2llepora, Tudbipora, Madre- 
pora etc. have a wide geographical distribution in the shallow warm waters of the tropical 
belt. It exhibits a great degree of variability in its form and habit due, probably, to the 
development of considerable powers of adaptation to the-variable conditions as regards strength 
of current, light, food supply and other features of the environment in shallow tropical waters. 
To divide the specimens of this genus into specific groups becomes increasingly difficult as 
our knowledge extends. 
The consideration of the fact that the individual colonies of these genera usually occur 
in great numbers and that there is nothing, so far as we are aware, to prevent constant cross 
fertilisation in shallow water, renders it probable that the shallow water specimens of each of 
these genera throughout the world represent only one true species. It has been shown that in 
the case of Mllepora”’) and Tudipora*) at least the anatomical structure of the colonies 
supports this conclusion. 
Stylaster however differs from some of the other genera of tropical zoophytes in the 
fact that it extends from very shallow into very deep water and it is interesting to note that 
the difficulty of arranging the deep sea specimens into specific groups is much less than in the 
case of the shallow water specimens. It would not be surprising if it were ultimately proved 
that in the case of Styaster isolation in deep sea localities has led to the differentiation of 
distinct species, in much the same way as isolation upon islands has led to the differentiation 
of species of terrestrial animals. In considering the systematic arrangement of any genus of 
zoophytes we must endeavour to distinguish between characters that are most probably modified 
by the immediate conditions of the environment and characters which are more stereotyped or 
fixed. In the genus Stylaster for example the shape assumed by the hydrophytum as a whole, 
its colour, its delicacy or robustness, the position of the calicles, the general texture of the 
surface etc. appear to be characters which are profoundly modified by the conditions of the 
environment. On the other hand the position of the ampullae, the character of the styles, the 
structure of the cyclosystems and many of the characters of the soft parts are probably less 
liable to modification by the direct action of the conditions of the environment. In the present 
state of knowledge and in the absence of any record of experimental work on the growth of 
corals the conclusions we reach may not prove to be satisfactory but we feel that it is only in 
1) S. J. Hickson, Proc. Roy. Dublin, Soc. VII, 5. 
2) S. J. Hickson, On the species of the genus Millepora. Proc. Zool. Soc. 1898. 
3) S. J. Hickson, A. naturalist in N. Celebes 1889, p. 129. 
