1884.] SPECIES OE OREASTER. 



CI 



When we oppose these facts to those which we have already learnt 

 as to the growth-changes in 0. armntus, we are met at once by the 

 obvious reflection that the very conditions of the case are exactly 

 reversed. In the one we have the progressive growth ; in the other 

 the as marked decline in the size of the spines. When we go 

 further and seek, as we are bound to do, for some explanation, we 

 find that, firstly, the explanation will probably be of this character: 

 Corresponding to the differences in the growth-characters of the 

 spines, there are differences in (a) the length of the free and 

 unprotected portion of the arms, which have become proportionately 

 shorter as the means of defence has been lost ; or (/3) there has 

 been a consolidation of the skeletal plates, which, becoming thereby 

 stronger, are the better able to withstand attacks from without. 



Either of these structural characters could be easily enough 

 investigated and demonstrated by a cabinet naturalist ; but in the 

 case now being studied there is not either that concentration or 

 consolidation, which nations as well as individuals have to suffer, 

 when their means of offence or defence are diminished or insufficient. 



An explanation must therefore be found in a study of living 

 specimens, with a view to see whether they are provided either with 

 protective colourings or offensive odours ; or in the examination of 

 the environment of the Starfish, and the possible absence of crea- 

 tures strong enough to prey on it. Should the latter be the case, 

 the comparatively rich development of spines in the younger forms 

 would be explained as due to the influence of heredity. 



In the classification and description of the species of Oreaster it 

 will, for the future, be necessary to bear in mind the two opposing 

 conditions represented by 0. armatus and O. occidentalis respec- 

 tively, and to endeavour to supplement the technical zoological de- 

 scription of the adult by a history of the growth of the species ; for 

 Starfishes, as for birds or monera, the life-history is an essential 

 factor in an intelligent arrangement. 



Speculations and considerations such as have here been briefly 

 sketched will not be barren of result if they direct the student of 

 living forms to the closer observation of environment, and to the 

 conviction that faunal lists and lists of collections have a scientific 

 value far above that of a mere catalogue, if to a knowledge of the 

 existence of a given species we can add something of its relations to 

 those other forms with which it lives, and on which it is as depen- 

 dent as are they on it. In this way some of the dangers of speciali- 

 zation may be diminished if not averted. 



I. List of the apparently distinct Species of Oreaster. 



1. affinis, M. Tr. 1 p. 46. 



2. alveolatus, Perrier, 2 p. 243. B.M. 



3. armatus, Perrier, p. 251. B.M. 



4. australis, Liitken, 3 1871, p. 252. 



1 M. Tr. = ' System der Asteriden ' by Miiller and Troschel. 



2 Perrier = Eevision des Stellerides par E. Perrier. 



3 Liitken =Videnskabelige Meddelelser, distinguished by the year. 



