^^"^ THE NEW EVOLUTION "^^^^ 



with various other butterflies, mostly with very 

 limited distribution. 



Other species, on the contrary, are so very highly 

 variable that they can only be defined in negative 

 terms. Being impossible of description, they can be 

 identified only by the fact that they do not conform 

 to the description of any other species. 



Such a species is one of the commonest feather-stars 

 (cf. fig. 43, p. 87) of the Indian and west Pacific 

 oceans which is found from Japan to Madagascar. In 

 this extraordinary creature the arms vary in number 

 from eleven or twelve to about seventy, but are usually 

 about twenty or about forty. The arms may be all 

 of the same length, or the hinder arms may be only 

 one-third as long as the anterior, or the anterior and 

 posterior arms may be of any intermediate relative 

 proportions. The arms may be short and stout, or 

 greatly elongated and attenuated; sometimes the ante- 

 rior arms are elongate and attenuated, and the poste- 

 rior short and stout. The pinnule combs may be long 

 and low, or short and high; they are usually confined 

 to the first two or three pairs of pinnules, but some- 

 times they occur at intervals almost to the arm tips. 

 The arm branches are typically of four segments each, 

 but usually one or more of them are of two segments, 

 and in rare cases all of them may be of two segments. 

 The leg-like processes on the dorsal side — the cirri — 

 may be numerous, rather stout, and well developed, 

 or they may be few and weak, or they may be alto- 

 gether absent. 



In Madagascar and in southern Japan this species is 



[132-] 



