682 REPORT— 1903. 



is remarkably plastic or accommodating to these epizoites, whereas iu others it is 

 resistant and rigid. 



The size and shape of the spicules have been taken as characters for the 

 determination of the species of Alcyonaria. It is true that in some species the 

 spicules are remarkably constant in size and shape, but in others they are extremely 

 variable. The remarkable torch-like spicules of the ccBnenchym of Eunicella 

 papillosa, the club-shaped spicules of Acrophytum, and the needle-shaped spicules 

 of many species of Pennatulids are remarkably constant in size and shape, but 

 in Sarcophytum, the new genus Sclerophytum, Siphonogorgia, Spongodes, and 

 a great many others, the size and shape of the spicules are extraordinarily vari- 

 able. In the matter of colour, too, we find the same thing. The genera Tubipora 

 and Heliopora are widely distributed iu the shallow waters of the tropical 

 seas and are very variable in many of their characters, and yet there is not a single 

 specimen of Tubipora known that is not red, nor a single specimen of Heliopora 

 that is not blue. The same may be said for several other species. On the other 

 hand, many specieg of Alcyonaria are extremely variable in colour. Thus, 

 Muricea chamceleon is, according to Von Koch, sometimes yellow, sometimes 

 red, and in some cases specimens show both red and yellow branches. The 

 specimens of Melitodes dichotoma in Cape waters are sometimes red and some- 

 times yellow. In a small species of Melitodes from the Maldive Archipelago 

 there is a very remarkable degree of variation in colour both in the nodes and 

 internodes, the details of which I have briefly described in vol. ii. of Mr. Gardiner's 

 Results. In the genus Chironephthya, also from the same Archipelago, the 

 variations iu colour are very remarkable, the spicules of the general coinenchym 

 showing various shades of red, pink, yellow, and orange, and the crown and 

 points purple, yellow, and orange colours which sometimes agree, but usually 

 do not agree, with the general colour of the ccEnenchym. The variability of the 

 genus is particularly interesting, as iu Siphonogorgia, the genus which comes 

 nearest to it, and is, in fact, difficult to separate from it, the colour of the 

 coenenchym is almost invariably red. 



To summarise this knowledge of variability in the Coelenttrata we may say 

 that we And either extreme plasticity or remarkable rigidity iu many of their most 

 important characters. Such important and essential organs as the tentacles, 

 stomodajum, mesenteries, &c., are in some groups very variable indeed, and in 

 others as stationary or fixed ; we find the same with organs such as the spicules of 

 Alcyonaria, which are, so far as we can judge, of less essential importance, and in 

 characters, such as colour, which must be, in the sedentary forms at least, of minor 

 importance. 



If we compare this with what we find in the higher groups of animals we 

 observe a great contrast. In fishes, to take an example at random, we may find 

 that in such characters as the size and weight of the adults, there may be great or 

 considerable variability, but in the essential organs, such as the heart, brain, and 

 stomach, there is almost complete rigidity. I do not mean by using the expression 

 'rigidity ' to imply that minor variations in size and shape do not occur, but that 

 major variations, such as a doubling of the stomach, a bifurcation of the cerebral 

 hemispheres or other variations, which it would be considered grotesque to sug- 

 gest even, do not and cannot occur. But even in minor characters, such as colour, 

 the possible range of variation in a fish is I'ar less than in Coelenterates. We may 

 find in the mackerel, for example, that individuals differ in the shade and range of 

 the green pigment, but we do not find in any species of fish that some individuals 

 are red, some yellow, some purple, &c. 



The contrast in this respect between the Coelenterate and the fish must be 

 associated with their diflerent degree of complexity of structure. In a complicated 

 organisation such as that of a fish, the brain, heart, and stomach must 

 mutually work together ; they must be co-ordinated in form and action. Any 

 profound variation or abnormality of one would interfere with the action of the 

 others and would therefore be incompatible with continued existence. In the 

 Coelenterate, however, the doubling of the siphonoglyph, the duplication or quad- 

 ruplication of the mesenteries does not, jn some cases, interfere materially wjth 



